Chocolate Streusel Filling and Topping
1/2 cup firmly packed light brown sugar
1 cup pecans
1 teaspoon ground cinnamon
2 oz bitter sweet chocolate chopped or 1/4 cup chocolate chips
1/4 cup flour
1/4 cup unsweetened cocoa powder
4 tablespoons unsalted butter

1) Place sugar, pecans and cinnamon in food processor. Cover and pulse until nuts are coarsely chopped. Transfer 3/4 cup of mixture to small bowl and stir in chocolate for filling. To remaining mixture in food processor add flour, cocoa powder and butter and pulse until mixture is crumbly for topping.

Sour Cream Coffee Cake
2 1/2 cups all-purpose flour
2 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/4 teaspoon salt
1 cup (2 sticks) unsalted butter, softened
1 1/2 cups granulated sugar
3 large eggs
1 large egg yolk
1 1/2 teaspoons vanilla extract
1 cup sour cream, at room temperature

1. Preheat oven to 325°F. Butter bottom and sides of 9-inch springform pan. Dust pan with flour, tapping out excess.
2. Sift flour, baking powder, baking soda and salt into medium bowl; whisk to combine and set aside.
3. Beat butter at medium-high speed in mixing bowl for 1 minute or until creamy, using electric mixer at medium-high speed. Gradually add sugar and beat at high speed until well blended and light, about 2 minutes. Add eggs and yolk, one at a time, beating well after each addition and scraping down sides of bowl as necessary. Beat in vanilla extract. Reduce speed to low and alternately add dry ingredients and sour cream, beginning and ending with dry ingredients and mixing just until combined.
4. Scrape half of batter into prepared pan and smooth top. Sprinkle with filling. Scrape remaining batter over filling and smooth top. Sprinkle with topping.
5. Bake 65 to 75 minutes or until toothpick inserted into center of cake comes out clean and cake pulls away from edge of pan. Let cake cool in pan set on wire rack for 10 minutes. Remove side of pan and cool completely.

AMAZING! I will definitely make this again and again. This will qualify you as a domestic goddess