Preheat oven to 350℉/180℃. Grease and flour a 10 inch tube pan or 9 x 13 inch pan.
In a medium bowl whisk together all purpose flour, baking powder, baking soda and salt. Set aside.
In a large mixing bowl cream together butter and sugar until fluffy, about 3 minutes. You can do this with an electric mixer or by hand. Add eggs, one at a time. Add vanilla.
On low speed (if using electric mixer), add flour and sour cream. Blend until just combined.
FOR THE CHOCO STREUSEL
In a small bowl combine brown sugar, all purpose flour, unsweetened cocoa powder and salt. Cut in butter with your fingers or a pastry blender until the mixture looks crumbly.
Spread batter into prepared pan and sprinkle evenly with streusel topping. Bake for 40-45 minutes or until a cake tester comes out clean. Cool cake in pan for at least 1 hour before serving.
Notes
Use half chocolate chips and half butterscotch chips for an amazing alternative.