Blend together the first 6 ingredients until smooth texture is formed. Add in the remaining cake ingredients and mix until all the lumps are gone, about 2 minutes.
Pour into a greased 13x9 deep casserole dish. Bake at 350 °F for 30-35 minutes or until toothpick comes out clean.
Remove cake from oven and set out entire dish on a wire rack.
Toppings
Blend together chocolate syrup and powdered sugar in a small bowl and set aside.
When cake is taken out of the oven, poke holes all over into cake with a straw. Don't poke the holes all the way through cake, only halfway.
Pour thickened chocolate syrup over the top of the hot and hole-filled cake. Let cake sit on wire rack to cool completely. When cooled, add marshmallow fluff to the top and keep cake in refrigerator.