Pre oven to 350°F.
Sift together flour baking powder and salt.
Beat egg whites and set aside

Cream butter and sugar. Add flour mixture and milk alternatively until combined. Fold in beaten egg whites with a rubber spatula. Spread in a well greased 9 by 13 baking pan.

Two separate bowl combine topping ingredients with a pastry cutter until crumbly. Sprinkle all over the top.
Bake for 40 to 45 minutes