Preheat oven to 350°F. Line a 9x5-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.
2¼ cups all-purpose flour, 2 teaspoons baking powder
In another small bowl, mix the granulated sugar and cinnamon together. Set aside.
½ cup granulated sugar, 1 tablespoon ground cinnamon
In a large bowl, whisk the eggs and brown sugar together. Add the milk, oil, sour cream, and vanilla. Whisk well.
2 large eggs, ½ cup brown sugar, ½ cup whole milk, ½ cup vegetable oil, ½ cup sour cream, 1 teaspoon pure vanilla extract
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.
½ cup all-purpose flour, ⅓ cup brown sugar, 2 teaspoons ground cinnamon, 3 tablespoons unsalted butter
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.