Butter and dust with flour, a medium sized bundt pan. You can also fill it in muffin cups (reduce the cooking time to half if doing so)

Mix together flour, baking powder, soda and salt together. Sift and keep aside.

Beat sugar and butter until light and fluffly.

Add eggs and egg whites one by one and beat well.

Add flour mixture and sour cream alternately and fold until well incorporated.

Spread half the mixture in the prepared pan and then sprinkle the streusel topping. Add the remaining batter.

Bake in preheated oven (180 degrees) for 30-40 mins.