Awesome sour cream coffee cake with brown sugar crumble topping. From the White Gull in in Fish Creek, Door County, Wisconsin, where they serve it in great big pieces. Use fresh or frozen fruit - fresh is better!
Preheat oven to 325°F Grease and flour one 8x12 pan, or use cooking spray.
Cream butter and sugar, add eggs, egg white, sour cream and vanilla and mix well.
In a separate bowl, mix flour, baking powder, and baking soda. Add to creamed mixture and mix well.
In another small bowl, combine topping ingredients until well mixed. Set aside.
Spread 1/2 of dough in bottom of prepared baking pan. Top with blueberries or cherries. Spread rest of dough on top (you may need to use your hands for this, the dough is sticky and can be tricky to spread).
Sprinkle topping over dough.
Bake at 325°F for 50 to 60 minutes or until toothpick inserted in center comes out clean.