In large bowl, beat together sugar and butter until creamy. Mix in Eggs, baking powder and salt. Alternate between adding in the flour and milk beating after each addition. Add Vanilla and stir until completely combined.
Pour batter into greased and floured 9x13 baking dish, and bake for 15-20 minutes.
Test with a tooth pick. When it comes out clean set cake aside and allow to cool.
In large bowl, cream together, Cream Cheese, Powdered Sugar and whipped topping. Evenly spread mixture over the top of the cooled cake.