Preheat oven to 400°F. Grease 12 muffin tins or use paper liners.
In a medium-sized bowl, whisk together the flour, baking powder, baking soda, and salt, and then set aside.
In another mixing bowl, beat the butter, sugars, and vanilla until creamy. Then beat in the eggs.
Add the banana and beat until combined.
Stir in the sour cream until mixed.
Add the flour mixture and stir by hand or at the lowest mixer speed until mixed, taking care not to overmix.
Fold in the chocolate chips and nuts. Divide the mixture between the muffin tins. The tins will be full. Sprinkle the coarse sugar over the muffins.
Bake for 18-20 minutes until golden brown or an inserted toothpick comes out clean.
Notes
Toasting Nuts
Toast pecans by placing them in a skillet and heating them on medium-low heat. Stir them until they are fragrant and beginning to brown, about 3 or 4 minutes. Remove them from the pan to cool so they will stop cooking. They will burn easily, so remove them from the heat before they get too brown.
Recipe Source
This recipe was adapted from Tate's Bake Shop Cookbook.