1. Preheat oven to 350°F.  Prepare a standard size jellyroll pan with parchment paper, just to cover the inside bottom. Spray paper and pan with non-stick baking spray. Set aside.
2. Prepare favorite cake flavor or mix according to instructions.  Spread into prepared pan evenly.  Bake for 19-22 minutes, or until springy or toothpick inserted in center comes out clean.  Remove from oven.
3. Allow cake to cool 10 minutes, then remove from pan to cool completely. Remove parchment paper.
4. While cake is cooling, prepare icing. Combine all icing ingredients in a medium metal or glass bowl.  Heat over a double boiler until smooth and just warm. Remove from heat.
5. Carefully halve the cake lengthwise, making two layers. This is easiest using a cake slicer or large serrated knife.  Remove top half of cake. Fill bottom layer with desired jam or frosting; replace top layer of cake.
6. Cut cake into one inch squares using a sharp knife or square cutter.
7. Place cake cubes on a cooling rack placed onto a rimmed pan. Pour icing over cake cubes, coating tops and sides. As icing begins to dry, lift each slightly from rack to make removal easier once fully dry.  Decorate as desired once cooled.
8. Keep in air-tight container until ready to serve.

*Note: Icing can be tinted with desired food coloring.