Step 1

Preheat oven to 350 degrees. Line a standard 12-cup muffin tin with baking cups. Spread walnuts on a baking sheet and bake until fragrant, about 12 minutes. Cool 15 minutes then coarsely chop. In a medium bowl, whisk together flour, baking powder, salt, and cinnamon. In a separate bowl, whisk together banana, sugar, eggs, butter, and milk. Stir wet ingredients into dry ingredients then stir in 1 cup walnuts.

Step 2

Divide batter evenly between prepared cups using a 2-ounce scoop. Sprinkle with remaining 1/2 cup nuts and sanding sugar if desired. Bake until tops spring back when lightly touched, about 20 minutes. Cool in pans 5 minutes, then remove to wire rack to cool completely.