Preheat oven to 350º.Place rack in the upper third of oven. Line a 13x9 pan with parchment paper. Spray lightly.
For the cinnamon Struesel topping: In a medium bowl. Whisk together the sugar , flour, cinnamon. Stir in butter. Until evenly coated. For the Brown sugar filling : mix all ingredients in a small bowl. Set aside.
For the Cake: Use an electric mixer with paddle. Beat together butter and sugars until well combined about 4 minutes. Add eggs one at a time. Beating 1 minute after each one. Scrape sides of bowl. In a small bowl whisk together flour, b. Powder, salt.In another bowl whisk milk and sour cream. Until combined.
With mixer on low. Add 1/3 of the flour mixture to the batter. As it is mixing add 1/2 of the milk mixture. Repeat until it is all in. Scrape down sides of bowl.
Spread 1/2 the batter on the bottom of your pan. Making sure you spread it ti edges Sprinkle your Brown sugar filling on top of the batter. Dallop the rest of your cake batter on top. Using a spatula spread batter across the pan. Using a knife gently swirl the filling into the batter.Sprinkle all of your topping mixture on top of your cake.
Bake 50 - 55 minutes. Or until cake is golden brown & toothpick comes out clean. Allow to cool. Cake wilk last 4 -5 days at room temperature.
