Step 1

Make streusel: Preheat oven to 350°F. Butter an 8 1/2-by-4 1/2-inch loaf pan; line with parchment paper, leaving a 2-inch overhang on long sides. Whisk together flour and brown sugar in a bowl combined. Add butter, peanuts, and salt. Stir with a fork until clumps form; chill.

Step 2

Make bread: Whisk together flour, baking powder, baking soda, and salt in a bowl. Whisk together bananas, brown sugar, granulated sugar, butter, and eggs until combined in a second bowl.

Step 3

Add wet ingredients to dry ingredients and stir until mixture is combined. Transfer to prepared pan; smooth top. Sprinkle with streusel.

Step 4

Bake until a toothpick inserted into center comes out clean, 50 to 60 minutes. Let cool in pan on a wire rack 10 minutes, then use overhangs to remove from pan and transfer to rack; cool completely.