1-Start by collecting all items like the 200 grams of cocoa powder and other listed ingredients, ensuring everything is at room temperature for easy mixing in this sour cream coffee cake recipe.

2-In a large bowl, combine the dry components such as 300 grams of flour, 100 grams of sugar, and 1 teaspoon of baking powder, stirring until well blended for your coffee cake.

3-Next, in a separate bowl, whisk together the wet elements including 2 cups of milk, 100 grams of butter, and 2 large eggs to create a smooth mixture for the coffee bake batter.

4-Now, gently fold the wet mixture into the dry one, then add in the cocoa powder for a chocolate twist, and pour the batter into a greased pan. Bake at 180 degrees Celsius for 30 minutes, checking with a toothpick for doneness, which makes this cinnamon crumb topping recipe truly moist.

5-While the cake bakes, prepare the buttery cinnamon crumb by mixing extra flour, sugar, and cinnamon, then sprinkle it on top midway through baking for added crunch. Once done, let it cool for 10 minutes before serving this homemade cinnamon crumb coffee cake to 8 people.