0 Preheat your oven to 350 degrees
1 Combine 1/2 cup of flour, 2/3 cup of brown sugar and 2 teaspoons of cinnamon in a small bowl and then add 4 tablespoons of melted butter and mix to combine into a loose crumble and set aside
2 In a large bowl, cream together 1 cup of room temperature butter with 2/3 cup of granulated sugar, 1/2 cup of brown sugar, 1 cup of sour cream and 2 teaspoons of vanilla extract with an electric hand mixer, stand mixer or stiff whisk
3 Add 2 large eggs and mix until fully combined and fluffy
5 In a small bowl, combine 2 cups of flour, 1 teaspoon of cinnamon, 1 teaspoon of baking powder and 1/2 teaspoon of salt in a small bowl
6 Add the dry ingredients into the wet ingredients and mix until all of the ingredients are just incorporated
7 Prepare an 9"x9" square baking pan or a 7"x11" rectangular baking dish by greasing the interior with softened butter or non-stick spray and lining the bottom with parchment paper
8 Transfer one half of the cake batter into the baking dish and spread half of the crumble evenly over the batter
9 Add the remaining batter and then top with the remaining crumble
10 Bake at 350 degrees on a middle rack for 50-55 minutes or until a toothpick comes out of the center of the cake clean
11 Allow the cake to cool in the baking dish on a cooling rack for 10 minutes
12 Carefully remove the cake from the baking dish and transfer it directly onto the cooling rack
13 In a small bowl, whisk together 1/2 cup of confectioners sugar with enough whole milk to create a thick, but pourable glaze (1-2 teaspoons)
14 Slice the coffee cake and drizzle with glaze
15 Serve warm
