1. Preheat the oven to 350 degrees and spray a 9×13 pan with non-stick cooking spray.

Streusel Topping

1. In a medium bowl, whisk together the granulated sugar, salt, flour and cinnamon. Add the melted butter and stir until combined. Do not break down the chunks. These chunks are what makes the pretty cinnamon goodness on the top of your coffee cake! Set aside.

Filling

1. In a small bowl, combine brown sugar, cinnamon and unsweetened cocoa powder. The cocoa powder is added to give the filling a deep color. You can’t really taste the cocoa powder. Set aside.

Cake

1. With a stand mixer, cream together the butter, salt, granulated sugar, and brown sugar, and baking powder, until smooth and creamy. Add in the vanilla extract. Add the eggs, being sure to incorporate each egg before adding the next.
2. In a medium bowl, combine the sour cream and milk and whisk together until well combined. Don’t bother breaking down all the clumps.
3. Alternating between each addition, add the milk mixture and flour into the cake batter and stir until the mixture is well combined between each addition. The batter will be thick and very smooth.

Assembling the coffee cake

1. Spread about 1/2 of the cake batter into an even layer on the bottom of the prepared pan. This should be about 3 cups.
2. Then, spread the filling mixture in an even layer on top of the batter layer.
3. Add the remaining cake batter on top of the filling mixture and spread into an even layer. Take a knife and make gentle swirls around the pan. You are not trying to mix it, but this will create a little bit of visual movement in the filling mixture.
4. Spread the topping mixture in an even layer on top of the cake.
5. Bake for 55-60 minutes, or until the top springs back when lightly touched in the middle and an inserted toothpick comes out clean.
6. Allow to cool for about 20 minutes before cutting and serving.