So yummy I have to stop myself from eating them all!
The ingredient list hides the physical density of this batter. Working with a stiff devil's food mixture requires precise handling because the dough resists standard mixing tools. Flour your hands before pressing two-thirds of the batter into the 13x9 inch baking pan to prevent sticking.
Thermometers fail here due to the varying layers of marshmallow and dense cake. Rely strictly on visual indicators to judge readiness. The initial ten-minute bake sets the lower crust until the edges look dry and matte. The final thirty-minute baking phase requires watching the dolloped surface carefully. The dropped spoonfuls of remaining batter should darken slightly and feel firm to a light fingertip touch, while the marshmallow layer underneath remains molten.