Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper.

Make the cake batter: In a medium bowl, whisk flour, baking powder, baking soda, and salt. In a large bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, beating well. Mix in vanilla.

Alternate adding dry ingredients and milk to the butter mixture, starting and ending with flour. Mix just until combined.

Divide the batter evenly between pans and bake for 25–30 minutes, or until a toothpick comes out clean. Cool in pans for 10 minutes, then turn out onto a wire rack to cool completely.

Prepare the frosting: Beat butter until creamy. Gradually add powdered sugar, then milk and vanilla. Tint the frosting with blue gel food coloring until you achieve Cookie Monster’s signature shade.

Assemble the cake: Level the cakes if needed. Place one layer on a cake board, spread a layer of frosting, then stack the second cake on top.

Frost the cake: Use the blue frosting with piping tip #233 to create a textured, furry look all over the cake.

Make the eyes: Use white candy melts or fondant balls and dot them with melted chocolate or an edible marker for pupils. Place on top of the cake at a slight angle.

Add cookies by cutting a small slit in the frosting and pushing mini cookies into Cookie Monster’s “mouth.” Scatter a few broken cookie bits for a fun touch.