Add milk and vanilla extract to a saucepan over medium-high heat.

Bring it to a boil, and then remove from heat.

Whisk together sugar and corn starch in a large mixing bowl.

Add egg yolks. Whisk until fluffy.

Add the hot milk mixture into the egg mixture gradually. Mix well.

Transfer everything back in the saucepan over medium-high heat. Stir constantly until thickened.

Remove from heat. Then add in butter, stirring constantly.

Let it cool and cover with plastic wrap. Chill in the refrigerator for about 2 hours.

Preheat oven to 400 °F. Line a baking sheet with parchment paper. Set aside.

Thaw the frozen puff pastry at room temperature. Unfold one sheet, and roll out to about 1/16 inch.

Cut the sheet into 2×4 inch rectangles using a kitchen knife. Place them onto the baking sheet, leaving about 2 inches apart.

Place another sheet of parchment on top and then cover with another baking sheet.

Bake for 10-12 minutes until golden brown. Repeat with the rest of the pastry.

In a large bowl, add powdered sugar, vanilla extract, and 3 tablespoons of milk. Whisk until combined. Transfer it to a piping bag and cut the tip off.

Pour 1/3 cup of the glaze into a separate bowl. Add cocoa powder and 1 tablespoon of milk. Whisk until combined. Transfer to a piping bag and cut the tip-off.

Spread vanilla glaze onto 9 pieces. Then pipe stripes chocolate glaze on top. Create a chevron pattern across the chocolate stripes by dragging a toothpick tip along the surface. Let the surface set.

Transfer the chilled pastry cream to a piping bag or zip-top bag. Pipe pastry cream onto one piece of cooked puff pastry without the glaze. Place another pastry on top. Pipe more pastry cream and add one piece with the glaze. Repeat with the rest of the pastry. Serve and enjoy!