Instructions:
Grease and flour a 13 x 9 x 2-inch baking pan. Spray with baking spray or grease and flour. Preheat the oven to 350°.
In a mixing bowl with electric mixer on low, combine the melted butter and buttermilk. Beat in the brown sugar, vanilla, and eggs until smooth and well blended.
Combine the flour, baking powder, and cocoa. Slowly stir into the butter and egg mixture then beat until well blended.
Spread in the prepared baking pan and bake for 25 minutes, or until the cake springs back when gently pressed with a finger.
Meanwhile, combine the topping ingredients in a saucepan and bring to a low boil. Cook, stirring frequently, for about 7 to 10 minutes, until thickened. Spread over the top of the hot cake and broil about 4 inches from the heat source for about 2 minutes, until bubbly and golden brown.
Serve warm with ice cream or whipped cream.