Preheat oven to 350°F (180°C). Liberally grease two 8″ round cake pans with vegetable shortening, and/or spray with baking spray.

Combine flour, sugar, baking powder, salt, and pudding mix in a large mixing bowl. Add in eggs and water, beating until smooth. Carefully add juice, melted butter, vanilla, and zest to the mix, mixing on medium speed until smooth.

Divide batter among prepared cake pans. Bake until golden and knife inserted into center of batter comes out clean and cake springs back – about 45-60 minutes. Allow to cool 10-15 minutes before turning cakes out onto baking rack to cool fully. Ideally, allow to cool to room temperature, wrap tightly with plastic wrap. Allow cake to sit overnight.

The following day, prepare Swiss meringue buttercream , divide into 3 equal portions. Add juice and zest of one orange to one portion, juice and zest of lemon to another portion, and lime juice and zest to the final portion. Use a tiny amount of food coloring to lightly tint each portion, if desired. Beat each portion of frosting until well combined and smooth. It WILL eventually come together!

To assemble cake:

Remove plastic wrap from cake layers. Carefully slice the domed top off each round, leveling the surface of the cake. Carefully cut each cake in half, horizontally, for 4 thin rounds of cake in all.

Place one round of cake on cake plate, spread with some of the lime buttercream. Top with another round, spread with some lemon buttercream. Top with a third round of cake, spread with some of the orange buttercream, and top with remaining layer of cake. Combine remaining amounts of buttercream to frost the outside of the cake. Serve at room temperature.