Add flour mixture and milk alternately just until combined. Do not over beat!
Fold in egg whites with a rubber spatula.
Grease a 9X13 baking pan. Or line it with foil or parchment paper and grease it well.
Use a pan with high sides.
In another bowl, combine topping ingredients with a pastry cutter until crumbly.
Sprinkle over top.
Bake 40-45 minutes, or until no longer jiggly in the center.
Notes
Make sure not to over beat, just combine. You do not want a rough and tough cake!
Folding in the stiff egg whites was a little more of an issue than I thought as my batter was very thick.
Recipe by I'm At Home Baking! at http://imathomebaking.com/best-coffee-cake/