• Preheat oven to 350°F (177°C). Grease and line a loaf pan with parchment.

Cinnamon Streusel (crumb topping):

• Mix 1 cup flour, 6 tbsp brown sugar, ¼ cup granulated white sugar, 2 tsp cinnamon and pinch of salt.
• Cut in cold butter until chunky crumbs form. Stir in vanilla paste if using. Refrigerate to keep cold while we prepare the batter.

Cinnamon-Sugar Swirl:

• Mix together the ¼ cup brown sugar and 1 ½ tsp of cinnaon. Set aside.

Banana Bread Batter:

• In a large bowl, whisk together melted butter, oil, and brown sugar until smooth.
• Whisk in eggs and vanilla until fully combined.
• Stir in mashed bananas and sour cream until smooth.
• Add flour, then sprinkle baking soda, baking powder, salt, and cinnamon on top of the flour. Use a spatula to gently fold everything together until just combined (don’t overmix).

Assemble:

• Pour half the batter into the prepared pan, then sprinkle evenly with the cinnamon-sugar mixture. Add the remaining batter on top and use a knife to gently swirl. Take the streusel mixture, squeeze it into clumps, and generously sprinkle over the batter to form a thick layer. Bake for 55–65 minutes, or until a toothpick inserted in the center comes out with just a few moist crumbs.
• Cool for 15 minutes in the pan, then transfer to a wire rack. Enjoy!