Mix flour, sugar, baking soda, baking powder, cocoa. Make three "nests" and put one of these in each nest: vinegar, vanilla, 5 tablespoons melted butter. Pour milk over all this and mix with spoon.
Bake in a greased 8" x 8" glass pan for 25 minutes in a 350° oven. While cake is baking, mix together brown sugar, 3 tablespoons butter, Pet cream. When cake is done, remove from oven and let stand for 5-10 minutes. Spread with icing. Place under broiler until done (2-3 minutes). Watch closely.