Preheat oven to 350°F.
Whisk together dry ingredients: flour, sugar, baking powder, baking soda, and salt.
Cut in butter with a pastry cutter (or two butter knives works as well).
Blend in eggs, beaten with sour cream. Mix well and set aside.
For the filling, in a small bowl, melt remaining butter (1 tablespoon).
Add in the rest of the ingredients: brown sugar, flour, cinnamon, and vanilla. Combine all ingredients until it becomes a damp sand texture.
Spray a bundt pan (or your pan of choice) with cooking spray on all sides.
Pour ½ of your sour cream mixture into the bundt pan. Sprinkle with the filling then cover with the remaining batter.
Bake 40-50 minutes in a 350° oven, being sure not to overcook. The coffee cake should be browned on top and a toothpick should come out clean when inserted into the center of the cake.
Enjoy!