Preheat oven to 350. Grease an 8-by-8 pan. Mix together flour, baking powder, salt, white sugar, cocoa. Add in milk, butter, liqueur and vanilla. Stir. Pat evenly into prepared pan. Mix together cocoa and brown sugar, making sure no lumps remain. Sprinkle on top of batter. Pour 1 cup plus a scant half-cup of boiling water over the top. Place in oven and bake for about 35 minutes.
Cool for about 5-10 minutes and scoop and serve. Best served slightly warm. It will be gooey. Serves 9-12.