Preheat your oven to 350 degrees F. Spray a 9×5 inch loaf pan with nonstick spray or line with parchment paper for easy slicing.

If you’re using nuts, toast them now. Spread chopped walnuts or pecans on a baking sheet and bake for 5-7 minutes, stirring every 2 minutes until fragrant.Set aside to cool.

In a large bowl or stand mixer, beat the butter until smooth. Add brown sugar and granulated sugar, then cream together for about 2 minutes until fluffy.

Add the eggs and vanilla, beating well until fully mixed.

In a small bowl, mash the ripe bananas with a fork or potato masher until you have about 1 cup. Add the mashed banana to the butter mixture and stir until combined.

Add 1 cup of flour to the bowl, but don’t stir yet. Blend the old-fashioned oats into a powder in a blender or food processor, then add the oat flour to the bowl without stirring.

Stir in 1 teaspoon baking soda, 1 and 1/2 teaspoons baking powder, and 3/4 teaspoon kosher salt into the dry ingredients.

Optional: add 1/4 teaspoon cinnamon, and 1/8 teaspoon each of nutmeg and cloves to enhance the flavor.

Combine the dry ingredients with the wet ingredients, stirring until just incorporated. Don’t forget to fold in 1/2 cup sour cream.

If using nuts, fold them into the batter now. Pour the batter into the prepared pan and smooth out the top.

Bake for 55-65 minutes. Check with a toothpick inserted into the center; it should come out clean or with very moist crumbs.

Allow the bread to cool on a rack for about 20 minutes before slicing.

Store covered at room temperature for up to 2 days. If there are leftovers, refrigerate or freeze for later.