Chocolate Babka

2 cups all-purpose flour
1/3 cup unsweetened cocoa powder
1 1/2 teaspoons baking powder
3/4 teaspoons baking soda
1 teaspoon ground cinnamon
1/2 teaspoon salt
1 cup unsalted butter
1 1/4 cups granulated sugar
1 teaspoon vanilla extract
3 eggs
1 cup sour cream

Topping:
1 cup semisweet chocolate chips
1 cup chopped pecans
1/4 cup granulated sugar
1 teaspoon ground cinnamon

Heat oven to 350 degrees F. Butter a 10-inch tube pan.

Sift together the flour, cocoa, baking powder, baking soda, 1 teaspoon cinnamon and salt; set aside.

In a medium bowl, beat the butter and 1 1/4 cups sugar with an electric mixer on high speed until light and fluffy. Change the mixer speed to medium, and beat in the vanilla extract. Beat in the eggs, one at a time. With the mixer on low speed, alternately beat the flour mixture and sour cream into the creamed mixture, beginning and ending with the flour mixture. Beat only until just blended.

For the topping: In a small bowl combine the chocolate chips, pecans, 1/4 cup sugar and 1 teaspoon cinnamon to make a crumb mixture. Spread half of the batter in the bottom of the prepared pan. Sprinkle with half of the crumb mixture. Pour in the remaining batter, and sprinkle with the remaining crumb mixture; press the crumbs in lightly so they adhere to the batter. Quickly, but gently cut through the batter and crumbs in an up and down motion with a knife. Lightly rap the pan once against a hard surface, to settle the batter.

Bake in the preheated oven for 40 minutes.

Cover the top of the cake with aluminum foil. Continue baking until a skewer inserted halfway between the side of the pan and the tube comes out clean, about 20 minutes longer. Cool the cake in the pan on a wire rack for 30 minutes. Carefully loosen the cake from the sides of the pan. Invert cake onto rack, and cool completely.