Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (flour through nutmeg) in a large bowl; make a well in center of mixture. Combine buttermilk, applesauce, 1 tablespoon butter, egg, and egg white in a bowl; add to flour mixture, stirring just until moist.
Spoon batter into a 9-inch round cake pan coated with cooking spray. Combine pecans and remaining ingredients in a small bowl; stir with a fork until mixture resembles coarse meal. Sprinkle evenly over top of cake. Bake at 350° for 35 minutes or until a wooden pick inserted in center comes out clean.