Preheat the oven to 350°F (190°C).
Prep the ingredients per the instructions above.
Mix the muffins: In a large bowl, mix together flour, baking powder, and salt. In another bowl, mash the banana with a fork, then beat in the sugar, cinnamon, egg, and vanilla. Stir the banana mixture into the flour mixture just until combined. Fold in the nuts.
Lightly grease a large muffin tin with nonstick spray or line it with muffin papers. Spoon batter into the greased wells evenly. Transfer to the oven to bake for about 20 to 25 minutes. While the muffins are baking, make the coffee.
Brew and prepare the coffee to your liking.
Check that the muffins are done by inserting a toothpick in the center. If it comes out clean, the muffins are done. If the toothpick has wet batter stuck to it, more cooking time is required. Cook a few minutes longer, then test again, until a toothpick inserted into the center of a muffin comes out clean. Remove from the oven and let cool for 5 minutes.
Serve the muffins with butter if using. Enjoy with coffee.