Cinnamon-crumble coffee cake

* 1 stick unsalted butter, softened

* 1 cup sugar

* 2 eggs

* 2 cups all-purpose flour

* 1 tsp baking powder

* 1 tsp baking soda

* 1 tsp vanilla

* 1 cup sour cream

* 1/2 cup chocolate chips

Topping

* 2/3 cup light brown sugar

* 1 tsp cinnamon

* 1 cup chopped walnuts (pecans would be good here, too)