Preheat oven to 350°F. Line a 9×5-inch loaf pan with parchment paper and spray it lightly with nonstick spray. Set aside.
In a small bowl, combine the flour and baking powder. Set aside.
In another small bowl, mix the granulated sugar and cinnamon together. Set aside.
In a large bowl, whisk the eggs and brown sugar together. Add the milk, oil, sour cream, and vanilla. Whisk well.
Add the flour mixture to the wet ingredients and mix just until combined.
Assemble the layered bread. Pour ⅓ of the batter into the loaf pan and spread it into an even layer. Sprinkle ⅓ of the cinnamon sugar on top. Repeat 2 more times, for a total of 3 layers of batter and 3 layers of cinnamon sugar.
Make the streusel. In a small bowl, combine the flour, brown sugar, and cinnamon. Add the melted butter and mix until the mixture comes together and forms small clumps.
Sprinkle the streusel over the top of the bread.
Bake for 60-65 minutes or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for 10 minutes before removing and transferring it to a wire rack to cool completely.