• 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 water and eggs, beating just until smooth. Carefully add melted butter and vanilla to the batter, mixing on medium speed until smooth.
• Divide batter evenly into two bowls. Add cocoa powder to one bowl, stirring until evenly distributed.
• Divide batter among prepared cake pans, one flavor per pan. 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.
• Prepare Swiss meringue buttercream. Run about ⅓ of the Oreo cookies through a food processor until finely ground. Crush another ⅓ of the package by hand, yielding medium/large chunks of cookies. Add cookie powder to frosting, stirring until well combined. Add cookie chunks, to taste – as many as you’d like.

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 chocolate cake on cake plate, spread with buttercream. Top with a round of vanilla cake, spread with buttercream. Top with second round of chocolate cake. Spread with a final layer of buttercream, and top with remaining layer of cake.
• Frost sides and top of cake with remaining buttercream. Garnish with remaining cookies, if desired. Serve at room temperature.