Beat eggs; add milk, flour, baking powder and salt. Butter two 8 or 9 inch round cake pans. Arrange slices of sausage and onion in the pans. Then pour batter over, dividing it equally between the 2 pans. Sprinkle cheese evenly over the batter. Bake at 400° for about 20 minutes or until golden brown. Serve hot. Cut in wedges and top with maple syrup, if desired.