Preheat oven to 350 F.
Grease an 8-inch pan, and line with parchment.
Stir all ingredients together very well, then spread into the pan.
If needed, use a second sheet of parchment to smooth down.
Bake 14 minutes on the center rack (some ovens require more baking time, so continue cooking until firm if needed).
Let cool completely before frosting.
