This may be the weightiest cake I’ve ever made. It all started with a birthday cake request – always the best ones because it usually means something unique – since we all want something special for our special days – not a plain white or chocolate cake, no simple layers of simple buttercream, no repeat flavors or styles. That’s why I LOVE birthday cakes. This one was no exception. The one flavor note I got for the order was tiramisu, but of course we wanted to go in the classic layer cake direction so those perfect Italian flavors were spun into a four-layer, 9-inch cake with the most frostings, fillings,…