Prepare Oven and Muffin Tin: Start by preheating your oven to 350°F (175°C). Line a standard 12-cup muffin pan with paper liners or lightly grease each cup with butter or non-stick spray to prevent sticking.
Mash Bananas and Mix Wet Ingredients: In a large mixing bowl, mash the bananas until smooth using a fork or potato masher. Stir in the sugar and egg, mixing until the mixture is well blended and slightly frothy. Then pour in the vegetable oil and stir until fully combined.
Combine Dry Ingredients with Walnuts: In a separate bowl (or directly into the banana mixture for simplicity), add the flour, baking powder, baking soda, salt, cinnamon, and nutmeg (if using). Add the ¾ cup of chopped walnuts at this stage—folding them in with the dry ingredients helps distribute them evenly without overmixing the batter.
Mix the Batter Gently: Fold the dry ingredients into the wet banana mixture just until no streaks of flour remain. Be careful not to overmix—this will ensure the muffins stay soft and tender.
Make the Walnut Sugar Topping: In a small bowl, stir together the remaining ¾ cup of chopped walnuts, brown sugar, and melted butter. Mix until all the walnuts are coated in the sweet buttery mixture. This will give the muffins a crisp, flavorful topping.
Fill Muffin Cups and Add Topping: Evenly divide the batter among the 12 prepared muffin cups. Spoon a bit of the walnut topping onto each muffin, spreading it out gently so it doesn’t clump in the center. This helps prevent it from sinking while baking.
Bake to Golden Perfection: Place the muffin tin in the preheated oven and bake for 20 to 23 minutes, or until the tops are golden brown and a toothpick inserted in the center of a muffin comes out clean.
Cool and Serve: Let the muffins cool in the tin for about 5 minutes, then transfer them to a wire rack to cool completely. Enjoy warm or at room temperature!