• Preheat the oven to 375℉/190℃ and line a 9x5 pan with parchment paper and and then set aside. In a small bowl mix together the cinnamon and brown sugar and set aside, this will be used later while layering.
  2 tbsp dark brown sugar, 1/2 tsp cinnamon

Make the streusel

• Combine softened butter, flour, brown sugar, cinnamon, and white sugar together with your hands or a fork until a crumbly streusel mixture forms. Set in the fridge to chill while the batter is being made.
  3/4 cups all-purpose flour, 5 tbsp unsalted butter, 1/4 cup white sugar, 1/4 cup dark brown sugar, 1/2 tsp cinnamon

Make the batter

• In a bowl, whisk together the flour, baking soda, cornstarch, and salt. Set aside.
  2 cups all-purpose flour, 1 tsp baking soda, 2 tsps cornstarch, 1/4 tsp salt
• In another large bowl, add the softened butter and white sugar. Cream together on medium-high speed for 2-3 minutes until pale and fluffy, scraping the sides as needed.
  1/2 cup butter, 3/4 cups white sugar
• Add in the eggs and vanilla and continue mixing until well combined, about 1-2 minutes.
  2 large eggs, 1 tbsp vanilla
• Starting with the flour mixture, add about 1/3 to the batter and mix until just combined. Then add 1/2 of the mashed bananas and mix again. Continue alternating, ending with the remaining flour (flour, bananas, flour, bananas, flour). Mix gently after each addition, being careful not to over-mix. You may use a spatula to mix in the last addition of flour to prevent over-mixing.
  1 1/4 cups bananas
• Add half of the batter into the prepared pan and spread evenly. Then sprinkle all of the cinnamon sugar on top, and a handful of the streusel (about 4-5 tbsps). Take the remaining batter and spread it evenly on top, without disturbing the layers below, then finish with the remaining streusel.
• Bake for 55-70 minutes, or until a toothpick inserted into the tallest point of the banana bread comes out clean with no wet batter. Allow to cool, then slice and enjoy!