How to Make It
Preheat oven to 350°F. Spray a 9-x5-inch loaf pan with baking spray; set aside.
To prepare the topping, whisk together 1 tablespoon sugar and ½ teaspoon cinnamon in a small bowl; set aside. To prepare the filling, whisk together 3 tablespoons sugar, 2 tablespoons flour, and 1 teaspoon cinnamon in a separate small bowl; set aside.
To prepare the bread, whisk together the flour, baking powder, cinnamon, and salt in a large mixing bowl.
Add the sugar to a medium mixing bowl; pour melted butter over sugar and whisk to combine. Whisk in both eggs until just combined. Whisk in sour cream and vanilla, mixing until just combined. Pour the sugar mixture over the flour mixture; gently stir with a rubber spatula until just combined.
Spread half of the batter into the prepared pan. Sprinkle the filling mixture evenly over top. Spread the remaining batter over filling mixture. Sprinkle topping mixture evenly over top of the loaf.
Bake 45-50 minutes or until a toothpick inserted into the center of the loaf tests clean. Allow to cool in the pan on a wire rack 10-15 minutes before removing loaf from the pan to cool completely.