Chocolate and Cinnamon Swirl Coffee Cake

This is another recipe I saved onto my desktop, from Chocolate Shavings. My desktop is filled with recipes I want to try but don't have time to make! I thought this would be a great thank you cake to make for Joey, the friend who designed my new logo!  Don't you love it!  I do!! Thanks Joey!  I also made him these chocolaty cookies.  I found that this recipe makes a lot of batter. So I had filled my loaf pan and then still had extra crumb topping and batter to fill up a ramekin and coffee mug, so I filled them, and baked them too! Thank god I had a cookie sheet under my loaf pan while it was baking, because literally I had a coffee cake explosion. Here's a picture of what the coffee cake baked in the mug looked like to give you an idea...looks just like a cup of coffee, doesn't it?! 

Chocolate and Cinnamon Swirl Coffee Cake
(recipe source: Chocolate Shavings, adapted from the Baked cookbook, although I made my cake in a loaf pan)
Crumb Topping
3/4 cup all-purpose flour
3/4 cup packed dark brown sugar
1/2 teaspoon salt
3/4 cup of hazelnuts
6 tablespoons cold unsalted butter, cut into 1 inch pieces

Chocolate Cinnamon Swirl
1/2 cup sugar
1 teaspoon dark unsweetened cocoa powder
1 1/2 teaspoons cinnamon

Cake
3 1/2 cups all-purpose flour
1 teaspoon baking powder
1 1/2 teaspoons baking soda
1/2 teaspoon salt
2 sticks unsalted butter, softened
2 cups sugar
4 large eggs
16 ounces fat free sour cream
1 1/2 teaspoons pure vanilla extract

Crumb Topping:
Put the flour, sugar, and salt in bowl of food processor and pulse to combine. Add the hazelnuts and pulse until they are finely chopped and incorporated. Add the butter and pulse until mixture looks like coarse sand. Cover and refrigerate.

Chocolate Cinnamon Swirl:
Mix ingredients in a small bowl and set aside.

Sour Cream Cake:
Preheat the oven to 350° F. Butter a 9×13-inch baking pan (whatever you use make sure not to fill it more than half way, the cake will overflow!!!) Sift together the flour, baking powder, baking soda, and salt together in a medium bowl.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter until smooth. Scrape down bowl and add sugar. Beat until the mixture is light and fluffy. Add the eggs, one at a time, beating well after each addition and scraping bowl as needed.
Add the sour cream and vanilla and beat just until incorporated. Add the dry ingredients in three additions, scraping down the bowl before each addition and beating only until each addition is just incorporated. Do not overmix.
Pour one third of the cake batter into the prepared pan. Use an offset spatula to spread batter evenly in pan. Sprinkle half of the chocolate cinnamon swirl mixture over batter and a third of the crumble topping, covering the entire surface of the batter. Spoon half of remaining batter over the swirl mixture and spread it evenly. Top with remaining swirl mixture and crumble topping, then the remaining batter, and spread the batter evenly. Sprinkle the remaining crumb topping evenly over the top of the batter.
Bake in the center of the oven for one hour, or until a toothpick inserted in the center of the cake comes out clean. Let the cake cool on a wire rack for 30 minutes.