diff --git a/apps/cookbook/src/components/external-link.spec.tsx b/apps/cookbook/src/components/external-link.spec.tsx
new file mode 100644
index 0000000..dcf7e75
--- /dev/null
+++ b/apps/cookbook/src/components/external-link.spec.tsx
@@ -0,0 +1,46 @@
+import { render } from '@testing-library/react';
+import React from 'react';
+import { expect, test } from 'vitest';
+import { ExternalLink } from './external-link';
+
+test(`${ExternalLink.name} renders correctly without UTM parameters`, () => {
+  const { container } = render(
+    <ExternalLink href="https://courses.marmicode.io">
+      Let's cook some tests
+    </ExternalLink>,
+  );
+
+  const linkEl = container.querySelector('a');
+
+  expect
+    .soft(linkEl)
+    .toHaveAttribute(
+      'href',
+      'https://courses.marmicode.io/?utm_source=cookbook',
+    );
+  expect.soft(linkEl).toHaveTextContent(`Let's cook some tests`);
+  expect.soft(linkEl).toHaveAttribute('target', '_blank');
+  expect.soft(linkEl).toHaveAttribute('rel', 'noopener noreferrer');
+});
+
+test(`${ExternalLink.name} renders correctly with UTM parameters`, () => {
+  const { container } = render(
+    <ExternalLink
+      href="https://courses.marmicode.io"
+      medium="in-article"
+      campaign="prep-station-v20"
+      content="flushing-flusheffects"
+    >
+      Let's cook some tests
+    </ExternalLink>,
+  );
+
+  const linkEl = container.querySelector('a');
+
+  expect
+    .soft(linkEl)
+    .toHaveAttribute(
+      'href',
+      'https://courses.marmicode.io/?utm_source=cookbook&utm_medium=in-article&utm_campaign=prep-station-v20&utm_content=flushing-flusheffects',
+    );
+});
diff --git a/apps/cookbook/src/components/external-link.tsx b/apps/cookbook/src/components/external-link.tsx
new file mode 100644
index 0000000..1c644be
--- /dev/null
+++ b/apps/cookbook/src/components/external-link.tsx
@@ -0,0 +1,42 @@
+import React from 'react';
+
+interface ExternalLinkProps {
+  href: string;
+  children: React.ReactNode;
+  className?: string;
+  medium?: 'footer' | 'in-article' | 'toc';
+  campaign?: string;
+  content?: string;
+}
+
+export function ExternalLink({
+  href,
+  children,
+  className,
+  medium,
+  campaign,
+  content,
+}: ExternalLinkProps) {
+  const url = new URL(href);
+  url.searchParams.set('utm_source', 'cookbook');
+  if (medium) {
+    url.searchParams.set('utm_medium', medium);
+  }
+  if (campaign) {
+    url.searchParams.set('utm_campaign', campaign);
+  }
+  if (content) {
+    url.searchParams.set('utm_content', content);
+  }
+
+  return (
+    <a
+      className={className}
+      href={url.toString()}
+      target="_blank"
+      rel="noopener noreferrer"
+    >
+      {children}
+    </a>
+  );
+}
diff --git a/apps/cookbook/src/components/special-offers.module.css b/apps/cookbook/src/components/special-offers.module.css
new file mode 100644
index 0000000..795b63e
--- /dev/null
+++ b/apps/cookbook/src/components/special-offers.module.css
@@ -0,0 +1,62 @@
+.container {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+
+  width: 80%;
+  max-width: 240px;
+  margin: 0 auto;
+  padding: 1rem;
+
+  border: 1px solid #e0e0e0;
+  border-radius: 8px;
+  background: #fdfcfb;
+}
+
+.link {
+  font-size: 0.8rem;
+  color: #6f2c91;
+  text-decoration: underline;
+}
+
+.primary {
+  font-size: 0.875rem;
+  font-weight: bold;
+}
+
+.image {
+  width: 100%;
+  border-radius: 4px;
+  margin-bottom: 0.5rem;
+}
+
+.priceInfo {
+  color: #666;
+  font-size: 0.82rem;
+  margin-bottom: 0.5rem;
+}
+
+.lifetimeAccess {
+  color: #333;
+}
+
+.description {
+  color: #333;
+  font-size: 0.8rem;
+  line-height: 1.2;
+  margin: 0;
+}
+
+.separator {
+  margin: 1rem 0;
+}
+
+.moreSeasoning {
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+}
+
+.moreSeasoningTitle {
+  font-size: 0.9rem;
+}
diff --git a/apps/cookbook/src/components/special-offers.tsx b/apps/cookbook/src/components/special-offers.tsx
new file mode 100644
index 0000000..99772fb
--- /dev/null
+++ b/apps/cookbook/src/components/special-offers.tsx
@@ -0,0 +1,72 @@
+import React, { JSX } from 'react';
+
+import styles from './special-offers.module.css';
+import { ExternalLink } from './external-link';
+
+export function SpecialOffers(): JSX.Element {
+  const medium = 'toc';
+  return (
+    <section className={styles.container}>
+      <ExternalLink
+        href="https://courses.marmicode.io/courses/pragmatic-angular-testing"
+        medium={medium}
+        content="course_image"
+      >
+        <img
+          src="/img/course.png"
+          alt="Pragmatic Angular Testing"
+          className={styles.image}
+        />
+      </ExternalLink>
+      <div>
+        <ExternalLink
+          className={[styles.primary, styles.link].join(' ')}
+          href="https://courses.marmicode.io/courses/pragmatic-angular-testing"
+          medium={medium}
+          content="course_link"
+        >
+          <span role="img" aria-label="cook">
+            👨🏻‍🍳
+          </span>
+          Let's cook some tests →
+        </ExternalLink>
+
+        <p className={styles.priceInfo}>
+          💰 80€ · <s>170€</s> ·{' '}
+          <span className={styles.lifetimeAccess}>Lifetime access</span>
+        </p>
+
+        <p className={styles.description}>
+          Learn how to write reliable tests that survive upgrades and
+          refactorings.
+        </p>
+
+        <hr className={styles.separator} />
+
+        <div className={styles.moreSeasoning}>
+          <strong className={styles.moreSeasoningTitle}>
+            <span role="img" aria-label="salt">
+              🧂
+            </span>
+            Need more seasoning?
+          </strong>
+          <ExternalLink
+            className={styles.link}
+            href="https://courses.marmicode.io/bundles/ginger-review"
+            medium={medium}
+          >
+            See code review/Q&A plans →
+          </ExternalLink>
+
+          <ExternalLink
+            className={styles.link}
+            href="https://courses.marmicode.io"
+            medium={medium}
+          >
+            Or let's plan a call →
+          </ExternalLink>
+        </div>
+      </div>
+    </section>
+  );
+}
diff --git a/apps/cookbook/src/components/youtube.spec.tsx b/apps/cookbook/src/components/youtube.spec.tsx
index b5035d2..3f70022 100644
--- a/apps/cookbook/src/components/youtube.spec.tsx
+++ b/apps/cookbook/src/components/youtube.spec.tsx
@@ -12,7 +12,7 @@ test(`${Youtube.name} should render iframe`, async () => {
   expect
     .soft(iframeEl)
     .toHaveAttribute('src', 'https://www.youtube.com/embed/aIAKlhrex8c');
-  expect.soft(iframeEl.style.aspectRatio).toBe('16 / 9');
-  expect.soft(iframeEl.style.width).toBe('100%');
-  expect.soft(iframeEl.title).toBe('Nx Implicit Libraries Video');
+  expect.soft(iframeEl?.style.aspectRatio).toBe('16 / 9');
+  expect.soft(iframeEl?.style.width).toBe('100%');
+  expect.soft(iframeEl?.title).toBe('Nx Implicit Libraries Video');
 });
diff --git a/apps/cookbook/src/css-modules.d.ts b/apps/cookbook/src/css-modules.d.ts
new file mode 100644
index 0000000..3d673e2
--- /dev/null
+++ b/apps/cookbook/src/css-modules.d.ts
@@ -0,0 +1,4 @@
+declare module '*.module.css' {
+  const classes: { [key: string]: string };
+  export default classes;
+}
diff --git a/apps/cookbook/src/theme/TOCItems/Tree.tsx b/apps/cookbook/src/theme/TOCItems/Tree.tsx
new file mode 100644
index 0000000..fe7688d
--- /dev/null
+++ b/apps/cookbook/src/theme/TOCItems/Tree.tsx
@@ -0,0 +1,16 @@
+import type { WrapperProps } from '@docusaurus/types';
+import { SpecialOffers } from '@site/src/components/special-offers';
+import Tree from '@theme-original/TOCItems/Tree';
+import type TreeType from '@theme/TOCItems/Tree';
+import React, { ReactElement } from 'react';
+
+type Props = WrapperProps<typeof TreeType>;
+
+export default function TreeWrapper(props: Props): ReactElement {
+  return (
+    <>
+      <Tree {...props} />
+      <SpecialOffers />
+    </>
+  );
+}
diff --git a/apps/cookbook/static/img/course.png b/apps/cookbook/static/img/course.png
new file mode 100644
index 0000000..0f7d4be
Binary files /dev/null and b/apps/cookbook/static/img/course.png differ
diff --git a/apps/cookbook/tsconfig.app.json b/apps/cookbook/tsconfig.app.json
new file mode 100644
index 0000000..3b7de78
--- /dev/null
+++ b/apps/cookbook/tsconfig.app.json
@@ -0,0 +1,10 @@
+{
+  // This file is not used in compilation. It is here just for a nice editor experience.
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "baseUrl": ".",
+    "composite": true,
+    "noEmit": false
+  },
+  "exclude": ["src/**/*.spec.ts", "src/**/*.spec.tsx"]
+}
diff --git a/apps/cookbook/tsconfig.json b/apps/cookbook/tsconfig.json
index 314eab8..d5aeac1 100644
--- a/apps/cookbook/tsconfig.json
+++ b/apps/cookbook/tsconfig.json
@@ -3,5 +3,14 @@
   "extends": "@docusaurus/tsconfig",
   "compilerOptions": {
     "baseUrl": "."
-  }
+  },
+  "references": [
+    {
+      "path": "./tsconfig.app.json"
+    },
+    {
+      "path": "./tsconfig.spec.json"
+    }
+  ],
+  "include": ["src/**/*.ts", "src/**/*.tsx"]
 }
diff --git a/apps/cookbook/tsconfig.spec.json b/apps/cookbook/tsconfig.spec.json
new file mode 100644
index 0000000..08f887c
--- /dev/null
+++ b/apps/cookbook/tsconfig.spec.json
@@ -0,0 +1,9 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "composite": true,
+    "noEmit": false,
+    "types": ["@testing-library/jest-dom"]
+  },
+  "files": ["test-setup.tsx"]
+}
diff --git a/apps/cookbook/vite.config.mts b/apps/cookbook/vite.config.mts
index 9811ba9..de70866 100644
--- a/apps/cookbook/vite.config.mts
+++ b/apps/cookbook/vite.config.mts
@@ -1,24 +1,8 @@
-/// <reference types='vitest' />
 import { defineConfig } from 'vite';
-
 import { nxViteTsPaths } from '@nx/vite/plugins/nx-tsconfig-paths.plugin';
 
 export default defineConfig({
   root: __dirname,
   cacheDir: '../../node_modules/.vite/cookbook',
-
   plugins: [nxViteTsPaths()],
-
-  test: {
-    globals: true,
-    environment: 'jsdom',
-    include: ['src/**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
-
-    reporters: ['default'],
-    coverage: {
-      reportsDirectory: '../../coverage/cookbook',
-      provider: 'v8',
-    },
-    setupFiles: ['./test-setup.tsx'],
-  },
 });
diff --git a/apps/cookbook/vitest.config.mts b/apps/cookbook/vitest.config.mts
new file mode 100644
index 0000000..0159660
--- /dev/null
+++ b/apps/cookbook/vitest.config.mts
@@ -0,0 +1,15 @@
+import { mergeConfig } from 'vitest/config';
+import viteConfig from './vite.config.mts';
+
+export default mergeConfig(viteConfig, {
+  test: {
+    environment: 'jsdom',
+    include: ['src/**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
+    reporters: ['default'],
+    coverage: {
+      reportsDirectory: '../../coverage/cookbook',
+      provider: 'v8',
+    },
+    setupFiles: ['./test-setup.tsx'],
+  },
+});
diff --git a/bun.lockb b/bun.lockb
index 42360c5..abf9c6f 100755
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