Preheat your oven to 350 degrees
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
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
Add 2 large eggs and mix until fully combined and fluffy
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
Add the dry ingredients into the wet ingredients and mix until all of the ingredients are just incorporated
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
Transfer one half of the cake batter into the baking dish and spread half of the crumble evenly over the batter
Add the remaining batter and then top with the remaining crumble
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
Allow the cake to cool in the baking dish on a cooling rack for 10 minutes
Carefully remove the cake from the baking dish and transfer it directly onto the cooling rack
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)
Slice the coffee cake and drizzle with glaze
Serve warm