Banana Bread with a Secret (Maybe?) Ingredient - A Duck's Oven

Ingredients

• 1/4 cup brown sugar
• 1 tsp ground cinnamon
• 1 tbsp flour
• 3/4 cup butter
• 3 cups white sugar
• 3 eggs
• 6 very ripe bananas, mashed
• 1 (16 ounce) container sour cream
• 2 tsp vanilla extract
• 2 tsp ground cinnamon
• 1/2 tsp salt
• 3 tsp baking soda
• 4 1/2 cups all-purpose flour
• 1 cup chopped walnuts (optional)