1/4 cup butter
1 1/2 cups confectioners' sugar
1 teaspoon cocoa powder
1 teaspoon vanilla extract
1 1/2 cups water
3/4 cup warm milk
3 tablespoons distilled white vinegar
1 egg
In a large glass bowl, mix butter, confectioners' sugar, cocoa powder, and vanilla.
Gently fold in the water. Stir flour into the mixture, then pour into the bottom of a 9x13 inch pan.
Bake uncovered in the preheated oven for 25 to 30 minutes. Refrigerate immediately after removing from pan. While the bars are baking, form the butter mixture and cocoa mixture and squeeze in egg.
Remove pan from oven, brush with milk and empty of remaining mixture.
Cool completely before cutting into bars. Cut into bars using a slotted motion using a wooden cutter or a series of slotted wooden cutters or, using your hands, 0.5 inch cut from each side of each bar. Cut each bar into 9 squares. Serve chilled or cut into bars for a smokey topping.