Preheat oven to 350°F. Grease a 9x5x2.5-inch loaf pan and line with parchment paper.

In a mixing bowl, combine mashed bananas, peanut butter, granulated sugar, light brown sugar, vegetable oil, eggs, and vanilla. Mix until thoroughly combined.

In a separate bowl, whisk together flour, baking powder, baking soda, and kosher salt.

Stir the dry ingredients into the banana mixture until just blended. Pour the batter into the prepared pan.

Drizzle the remaining 2 tablespoons of peanut butter over the top of the batter. Use a skewer or chopstick to swirl the peanut butter into the top of the bread.

Bake in the preheated oven for 70-75 minutes or until a toothpick inserted in the center comes out clean. Check around the 60-minute mark; if deeply golden, tent lightly with foil.

Let cool in the pan for about 10 minutes before using the parchment paper to lift out onto a cooling rack. Allow to cool completely before slicing.