Heat oven to 350. Have an ungreased 9 inch square baking dish ready.

Mix flour, sugar, 1/4 cup cocoa powder, baking powder, and salt in a medium bowl. Stir in milk and vanilla until well blended. Spread in pan.

Sprinkle with brown sugar and the remaining 3 tablespoons cocoa. Pour boiling water over surface. Bake 40 minutes or until top looks dry. Cut in to 9 squares. Serve warm.