Step #2 To prepare streusel, mix first 3 ingredients in a small bowl; set aside.
Step #3 To prepare cake, butter, beat 2 c sugar, & cream cheese at medium speed of a mixer until well-mixed (about 5 mins).
Step #4 Add egg whites & egg, 1 at a time, beating well after each addition.
Step #5 Lightly spoon flour into dry measuring c; level with a knife.
Step #6 Combine flour & next 3 ingredients (flour through salt), stirring well with a whisk.
Step #7 Add flour mixture to sugar mixture alternately with sour cream, beginning & ending with flour mixture.
Step #8 Stir in vanilla.
Step #9 Spoon half of batter into bottom of a 12-c Bundt pan coated with cooking spray; sprinkle with streusel.
Step #10 Spoon remaining batter over streusel; spread evenly.
Step #11 Bake at 350° for 1 hr or until a wooden pick inserted in center comes out clean.
Step #12 Cool in pan 10 mins on a wire rack; remove this from pan.
Step #13 Cool completely on wire rack.
Step #14 Sprinkle top with powdered sugar.
Step #15 Note: We also tested this cake substituting 1 c light butter (such as Land O Lakes) for 10 tbsps regular butter.
Step #16 Because the total fat was slightly lower using light butter, we discovered we could increase the walnuts from 1/4 c to 1/2 c & still have about the same amount of calories & fat.