Cream the sugar and butter together. Add the egg and milk and mix with an electric mixer until well blended. Dump in the sifted flour, baking powder and salt. Mix together until smooth, but be careful not to over mix.
Melt the butter over low heat in a saucepan. Add the flour, brown sugar, and cinnamon. Mix well, but it's ok if it's kind of lumpy.
Grease an 8x8 inch square pan. Pour half of the batter (which should be a little bit doughy) and spoon half the struesel over the batter. Cover with the rest of the batter and top with the rest of the struesel.
Bake at 375 F for 25-30 minutes. Cool on a wire rack, then cut.