Mix cake according to manufacturer’s instructions. Measure out 4 pounds batter, deposit 1 pound into a sprayed and papered 8-inch cake pan. Repeat three times to make 4 cakes total. Bake at 350F until cake springs back lightly when touched. Let cool completely. Once cooled, trim the bellies of each cake, saving them for other uses. Place one cake round on a cake board, pipe buttercream around the edges. Using a #4 grey scoop, place one scoop strawberry filling on the cake round and spread to edges and place another cake round on top. Repeat with the next layer, filling the next layer with raspberry filling, and the top layer with blueberry filling. Place internal supports/dowels into the cake. Crumb coat with buttercream, smooth ice, then gently dab granola on the bottom half of the cake. Decorate the top with fresh fruit.