Mix together cake batter and pour into 3 separate cake rounds. Bake according to package directions and allow to cool.
To make the classic buttercream, whip the butter in a large mixing bowl with an electric mixer. Slowly add in 2 cups of powdered sugar. Mix until combined. Add the vanilla and 2 more cups of powdered sugar and continue mixing. At this point you may need to add a teaspoon or two of milk to thin the frosting down. Slowly add in your last 4 cups of powdered sugar and mix until combined. Add more or less milk depending on the consistency. You want the frosting to be thick, creamy and to be able to hold a point.
Divide the frosting into 3 bowls.
For the strawberry buttercream, place 1/3 of the frosting back in the mixing bowl and mix in the strawberries. Add in an additional 1 cup of powdered sugar (more or less if needed) to thicken and mix until smooth.
For the chocolate buttercream, add the cocoa powder to the bowl of classic buttercream and stir. Add 12 chocolate kisses to a microwavable bowl. Melt in the microwave for 1 minute at 50% power. Stir until melted. Cook an additional 20 seconds if needed. Then stir into the frosting and mix until smooth.
To frost the cakes, place one layer of chocolate cake onto a cake stand or plate. Then add a thick layer of the strawberry frosting to the center of the cake, reserving some of the edges. Then add the second layer of cake and frost with the plain buttercream frosting, reserving some for the edges. Then add the third layer of cake and frost the top with the chocolate frosting. I like to use a 1M frosting tip to fill in the gaps between each layer with frosting and to add some decorative flowers along the top edge. Next, place chocolate kisses along the top edge of the cake and add sprinkles to the center of the cake.
Keep refrigerated until ready to serve.
Can use other types of cake, like vanilla, yellow or strawberry.
I like to place my cake rounds in the refrigerator for about 2 hours before frosting.