Preheat oven to 350F degrees. Gather your ingredients so that you have everything close at hand on the counter or table.
Prepare the Ingredients
Using a blending fork, mash the ripe bananas in a medium-sized bowl.
Chop the English walnuts (or pecans) with a nut chopper or with a knife and cutting board.
Place 1/2 cup coconut flakes on a baking sheet and toast in the oven for 5-7 minutes until lightly browned. Set aside until ready to use when topping the muffins.
Prepare the Batter
In a large mixing bowl, combine the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Whisk until everything is combined. Create a hole in the center of the flour.
Spoon the sourdough starter into a medium bowl. Add in the whole milk, vegetable oil, large egg, and vanilla extract. Mix together to combine.
Pour the sourdough mixture into the center hole you made with the flour. Using a rubber spatula or batter whisk, gently mix the batter to combine, but don't overmix.
Fold in the mashed bananas, chopped nuts, and remaining coconut flakes until incorporated with the batter.
Bake the Muffins
Spray the muffin cups with baking spray. Or, if desired, you may line a regular-sized muffin tin with paper liners.
Spoon batter into the muffin cups, filling about 2/3 full, or use a large cookie scoop to fill the cups.
Sprinkle each muffin top with two teaspoons of toasted coconut flakes.
Bake in preheated oven for 25-30 minutes, until the tops are lightly browned and muffins spring back when touched on top.
Cool for 5-7 minutes and then transfer muffins to a wire cooling rack.
Serve warm with butter or even honey butter. Serves 12