Cinnamon Coffee Cake2018-01-18
Preheat oven to 350°F. Butter 8″ square baking pan; set aside. Toss hazelnuts, chocolate, cinnamon, and 1/4 cup sugar in a bowl. Whisk flour, baking powder, baking soda, and salt in a medium bowl. Using an electric mixer on high speed, beat butter and remaining 3/4 cup sugar in a large bowl until light and fluffy, about 3 minutes. Beat in vanilla. Add eggs one at a time, beating to blend between additions and occasionally scraping down sides of bowl. With mixer on low speed, add dry ingredients in 3 additions, alternating with yogurt in 2 additions, beginning and ending with dry ingredients. Pour half of batter into prepared pan and smooth top; top with half of hazelnut mixture. Spoon remaining batter over and smooth top; top with remaining hazelnut mixture. Bake cake until top is golden brown and a tester inserted into the center comes out clean, 4045 minutes. Transfer pan to a wire rack; let cake cool in pan before turning out. DO AHEAD: Cake can be made 1 day ahead. Store airtight at room temperature.