Prepare your favorite cake recipe — divide the batter between 8 or 9-inch round cake pans. Bake and cool the cake rounds. Once the pans are cool enough to touch, transfer the cakes to a wire rack and allow the cakes to completely cool before you begin decorating.
Make one large batch of buttercream. Beat the butter for a few minutes on medium speed, preferably using a stand mixer with the paddle attachment. On slow speed, gradually add the confectioners' sugar 1 to 2 cups at a time, allowing each batch of sugar to incorporate with the butter before adding the next. Increase the speed to medium and add the vanilla, cream and salt. Beat for an additional 3 minutes.
From here, divide and color the buttercream according to the below:
Blue Buttercream Frosting: Add 2 cups of the buttercream into a bowl and color with blue food coloring. Add the frosting into a plastic piping bag. Use a rubber band to close.
White Buttercream Frosting: Insert a small round tip into a plastic piping bag, add 1 cup of frosting to the bag and close the bag with a rubber band. Divide the remaining frosting amongst plastic piping bags. Optional: To make the exterior frosting process easier, use a large basketweave decorating tip.
Additionally, set aside your lemon extract, unused cosmetic sponges, and the blue food colorings.