Prepare the cake batters individually in two separate bowls. In 3 (6x6x3) cake pans or 3 round cake pans fill 2 pans with red velvet mix and 1 pan with yellow butter batter.*Note: there will be excess yellow butter batter left* Bake as directed on the boxes and after finished baking, allow to cool for 1 hour before continuing to the next step.
After cooling, remove from pans and use a knife to slice off any uneven parts on the base and top of the cakes and set that to the side. When the cakes are cooled and evened out, place your first red velvet layer on a plate or serving platter. Spread your raspberry puree on top of the first layer cake from side to side and place your yellow butter layer on top. Spread more of the raspberry puree on top of that layer and place your final red velvet layer on top. Once you have your layers in line and even you can then put the icing on the cake.
Prepare the icing by removing from the container and stirring with a spoon vigorously for 1 minute to soften the icing and make it easier to spread. Finally, spread the icing on the sides and top of the cake and decorate as desired. For the best results, store cake in the refrigerator until serving so the raspberry puree stays cool.