The Best Coffee Cake. Ever.

Preheat oven to 350 degrees. Sift together flour, baking powder, and salt. Beat egg whites and set aside. Cream butter and sugar. Add flour mixture and milk alternately until combined. Don't overbeat. Fold in beaten egg whites with a rubber spatula. Spread in a well-greased 9 x 13 (or LARGER!) baking pan. A cake pan with higher sides would be best.In a separate bowl, combine topping ingredients with a pastry cutter until crumbly. Sprinkle all over the top.Bake for 40 to 45 minutes, or until no longer jiggly. Serve warm—delicious!