Chocolate-Cinnamon Coffee Cake

Ingredients

• ½ cup (1 stick) unsalted butter, room temperature, plus more for pan
• ½ cup blanched hazelnuts, chopped
• 2 ounces bittersweet chocolate, chopped
• ¾ teaspoon ground cinnamon
• 1 cup sugar, divided
• 2 cups all-purpose flour
• ¾ teaspoon baking powder
• ½ teaspoon baking soda
• ¼ teaspoon kosher salt
• 1 teaspoon vanilla extract
• 2 large eggs
• 1 cup plain whole Greek yogurt

Steps

1. 8" square baking pan
2. Preheat oven to 350°. Butter 8” square baking pan; set aside. Toss hazelnuts, chocolate, cinnamon, and ¼ cup sugar in a bowl.
3. Whisk flour, baking powder, baking soda, and salt in a medium bowl. Using an electric mixer on high speed, beat butter and remaining ¾ 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.
4. 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, 40–45 minutes. Transfer pan to a wire rack; let cake cool in pan before turning out.
5. DO AHEAD: Cake can be made 1 day ahead. Store airtight at room temperature.