I've been playing with making filled cupcakes and layered cakes recently and it has been a very yummy experimentation process, even if some results weren't quite as pretty as I would have liked. In my experimentation, this is the method that I came up with that makes a two layer cake with filling a breeze!
For this particular cake, I had two round yellow cakes, blueberry filling and lemon frosting. When I made the frosting, I pulled out about 1 cup of the frosting that was thicker, before I had added enough of the liquid to the frosting to make it easily spreadable. Here's the step by step.
1. Slice the top off the cake that will be the bottom layer so that it is as smooth and flat as possible and position it on your tray.
2. Take the thick frosting and put it in a plastic sandwich bag or piping bag if you have one. Cut the corner of the bag so that it makes a 1/4 inch opening. Pipe the frosting around the edge of the bottom cake layer creating a wall of sorts to hold your filling in.
3. Spoon and spread your filling onto the cake.
4. Add top layer of cake. The frosting wall oozed a little bit but the blueberries stayed right in the middle where I wanted them. The frosting that oozed was easily spread as part of the step 5.
5. Frost the cake with a thin layer of icing to keep all the crumbs in place.
6. Frost with a thick layer of icing to cover the cake.
7. Slice and enjoy!