Aquamarine-Inspired Lemon Birthday Cake

Heat oven to 350°F. Grease and flour two 6-inch round cake pans.  

Prepare cake batter as directed on the package. Divide batter evenly between pans.

Bake 35 to 40 minutes, or until a toothpick inserted into the center comes out clean. Cool 10 minutes; remove from the pans and place on a cooling rack. Cool 30 minutes at room temperature. Place cake layers in the freezer for 20 to 30 minutes or until chilled but not completely frozen.

In a large bowl, beat softened butter with an electric mixer on medium-low speed for 2 to 3 minutes or until smooth and creamy. Add powdered sugar in batches, beating until smooth after each addition. Add vanilla, beat until well blended.

In small bowl, mix 1/2 cup of the frosting with about 3 drops of blue gel food color until well blended; set aside. 

Using a serrated knife or a cake leveler, cut rounded tops off cake layers to create a level surface.

Spread a layer of the white frosting on top of one of the cake layers; top with the second cake layer. Spread a thin coat of white frosting over entire cake to lock in the crumbs. Freeze for 10 minutes.

Frost the entire cake with another coat of white frosting.

Frost one half of the cake with a layer of the blue frosting. Use an offset spatula to swirl in small amounts of white frosting and create the texture of waves throughout the blue frosted side of the cake.

Create seashells out of the fondant by placing small amounts of fondant into seashell fondant molds. Let fondant sit in molds for 10 minutes or until the fondant becomes firmer and shapes can be removed from the mold. Place seashells on the cake as desired.