Read through the full directions and watch my Elmo Cake video tutorial before beginning. (Same method here, just no nose.) If you wish to make the cake ahead of time, read my Make-Ahead Instructions below before beginning.

Preheat oven to 350°F (177°C). Grease two 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper. Parchment paper helps the cakes seamlessly release from the pans. (If it’s helpful, see this parchment paper rounds for cakes video & post.)

Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.

Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter and sugar together on high speed until creamed, about 3 minutes. Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the egg whites, sour cream, and vanilla. Beat on high speed until fully combined and mixed, about 2 minutes. Scrape down the sides and up the bottom of the bowl as needed. Pour the dry ingredients into the bowl. Then with the mixer running on low, slowly pour in the milk. Do not over-mix. You may need to whisk it all by hand to make sure there are no lumps at the bottom of the bowl. The batter will be slightly thick.

Toss mini chocolate chips with 1 Tablespoon of cake flour to coat them and then fold into the batter.

Pour batter evenly into cake pans. Bake for around 25-26 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake. If it comes out clean, the cake is done. Cool cakes in the pans set on a wire rack for 30 minutes, then remove the cakes and cool completely directly on a wire rack. The cakes must be completely cool before frosting and assembling.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy, about 2 minutes. Add confectioners’ sugar, milk/cream, vanilla extract, and salt with the mixer running on low. Increase to high speed and beat for 3 full minutes. Taste. Add a pinch of salt if frosting is way too sweet. Frosting will be thick.

Place 1 cup + 2 Tablespoons (about 1 heaping cup or 275g) of frosting into a medium bowl. This will remain white/untinted and be used for the cake’s filling and to form Cookie Monster’s eyes. Place 1/3 cup (about 85g) of frosting into a small bowl. Stir in 3 drops of black gel food coloring until it’s dark gray. (Keep in mind that frosting dries darker.) Tint the remaining frosting blue using about 4-5 big drops of blue gel food coloring. Tint until you are satisfied with the color. Remember, frosting dries darker, and we’re going for lighter Cookie Monster blue, not darker Grover blue!

Using a large serrated knife, slice the domes off the cooled cakes (a semi-thin layer) to create a flat surface. Place tops into a bowl to use in step 10. Place 1 cake layer on your cake stand, serving plate, or cake turntable. Spread 1 cup (about 250g) of white untinted frosting all over the top. (Reserve remaining white frosting for step 10.) Top with 2nd layer. Spread a thin layer of blue frosting around the sides and top of the cake. This is your crumb coat and should be a pretty thin layer. An icing spatula and bench scraper are helpful for this. Chill uncovered in the refrigerator or freezer for at least 30 minutes to help set the crumb coat.

Crumble the pieces of cake that you leveled off into crumbs. I just use my hands for this. Stir in 1 Tablespoon of white frosting. If the mixture still seems pretty crumby and dry, add a little more of the white frosting until you have a moist mixture that you can form into shapes. Mixture shouldn’t be overly wet. Form into two 2-inch discs. Smooth them out as best you can. Place on a lined baking sheet and chill in the refrigerator or freezer for at least 30 minutes to set. Once they’re set, you can smooth out any bumps on the surface with your hands if needed.

First, spread a thin layer of black frosting on the bottom half of the top of the cake. Use a small offset spatula to help ensure it’s perfectly smooth. Reserve remaining black frosting. Using a toothpick, trace/outline Cookie’s mouth shape within the black frosting. Use it as your guide for piping his fur around it. Fit your piping bag with Wilton piping tip #233 (grass tip). Spoon some blue frosting inside. It’s difficult to pipe this frosting if the bag is over-filled, so just work with a little bit of frosting in the bag at a time. Place the tip directly on top of the cake’s surface and apply pressure to squeeze the frosting out of the tip. Quickly lift the tip up while squeezing the frosting out. Pipe his fur all over the top and sides of the cake. (The sides are optional, but if you have enough frosting, go for it!) It’s helpful to carefully tilt the cake stand/turntable so you can more easily pipe frosting on the sides. Set cake aside. You can refrigerate uncovered if desired as you finish Cookie’s eyes.

Melt the white chocolate and oil together in a double boiler or the microwave. If using the microwave: place the chopped chocolate and oil in a medium heat-proof bowl. Microwave for 20-second increments, stirring after each time, until completely melted and smooth. Place one of the discs (eyes) into the white chocolate. Use a fork to help fully coat it. Using a fork, lift the disc (eye) out of the chocolate. Place back onto lined baking sheet. Repeat with 2nd disc (eye). Refrigerate or freeze for 20 minutes or until white chocolate has set.

After the white chocolate sets, fit your piping bag with Wilton tip #12 (round tip). Spoon some black frosting inside. Pipe Cookie Monster’s pupils onto the eyes—remember to make them off-center and “googly”. Carefully press the eyes on top of the cake to form Cookie’s face. If desired, add chocolate chip cookies around the cake and in his mouth, see Note.

If you decorated the cake on a cake turntable, use a couple thin spatulas (and a helper!) to carefully lift the cake off the turntable and onto a cake stand, server, or cake carrier base. I actually like to use a cake carrier to cover and store my cakes in the refrigerator.

Cover leftover cake tightly and store in the refrigerator for up to 5 days.