1) Into a mixing bowl sift together the flour, baking powder, salt, and sugar. Cut butter into the dry ingredients with a fork or pastry blender. In a separate bowl combine egg with milk; add to flour mixture. Stir until mixture is well blended and smooth. Spoon into a greased and floured 9-inch layer pan. Spread dough evenly. Brush top of dough with melted butter.
2) Combine sugar, flour, and cinnamon; sift over the top of the cake, spreading with a fork to cover dough evenly. Bake at 400° for 25 to 30 minutes. Cut coffee cake in wedges; serve warm from the pan.