Beat with an electric mixer until smooth and thick. To make the cake place the sourdough starter in a bowl.
Crumble topping ingredients together i use a pastry blender and sprinkle topping on top of batter.
Sourdough coffee cake. In a large mixing bowl use a spatula to cream the butter light brown sugar and granulated sugar until smooth. Smooth top and sprinkle reserved crumbs evenly over the batter. Combine sourdough starter oil and egg.
Combine sourdough starter flour sugar oil baking powder salt and cinnamon in a bowl. Pour the batter into a buttered and floured 8 or 9 inch square pan or an 8 inch round layer cake pan. Stir together dry ingredients and add to sourdough mixture.
Sprinkle topping over the cake batter. Bake for 35 minutes at 350 degrees. Preheat oven to 375 f.
Pour batter into the prepared pan. Put dough into greased 9 inch square pan. Lightly grease an 9 x 9 metal baking pan with butter or cooking spray.
Mix brown sugar softened butter and cinnamon in a bowl until evenly moistened. Add the rest of the ingredients and stir until combined. Sourdough coffee cake batter preheat your oven to 3500f 1750c.