Preheat over 350 degrees spray a 8x8 baking dish with cooking spray
In a medium bowl (or a food processor) combine the topping ingredients just until slightly clumpy and set-aside
In a large bowl and using a mixer cream butter and sugars together until combined, add eggs one at a time than milk, sour cream, and vanilla and mix just until combined.
In a small bowl mix the flour. baking powder and salt then add it to the wet ingredients. mix until just combined.
Pour half of the cake batter into the prepared baking pan. Gently spread half the crumb mixture over the cake layer pressing gently. Carefully spread the remaining cake batter over the crumb mixture followed by the rest of the crumb mixture.
Place cake in the center of the oven and bake for 40-45 minutes or until toothpick inserted in center comes out clean.
Let cool and sprinkle powdered sugar (confectioners sugar) on top if desired
Video
Notes
Use full-fat sour cream, you can also use Greek yogurt.You can double this crumb cake and bake it in a 9x13 baking pan.Spoon flour into your measuring cup then level off with the flat end of a knife.To spread the top layer of batter without lifting it from the cinnamon sugar layer, Spray a rubber spatula with non stick cooking spray.