It's actually rather simple. Here's what I did. First I made the cake. I just used a box cake recipe, in this case it was a red velvet cake. I also got a quart of ice cream. I chose Black Raspberry Chocolate Chunk.
I baked the cake in a bread pan. After it had cooled, I removed it from the pan and cut the rounded part off the top so I had a flat surface on both sides. After cleaning the bread pan, I lined it with plastic wrap and packed the ice cream into it. I put my cake on top of the ice cream, covered the whole thing and put it in the freezer for about 6-8 hours.
When I was ready to make it, I set the oven to pre-heat to 500 degrees. I made some meringue (I used 5 eggs) while the oven was heating. I took the ice cream/cake combo from the freezer and inverted it onto a cookie sheet lined with aluminum foil (cake-side down, ice cream up). I peeled the plastic wrap from the ice cream and coated the entire thing in meringue.
Then I stuck it in the oven for 3 minutes.