Preheat the oven to 350°F (190°C).
Prep all muffin ingredients per the instructions above.
Mix and bake the muffins: In a large bowl, measure out and mix together flour, baking powder, and salt. In another bowl, beat together bananas, sugar, cinnamon, egg, vanilla, and melted butter. 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 muffin tin to fill them about 3/4 of the way. Transfer to the oven to bake for about 20 minutes. While the muffins are baking, make the coffee.
Make the coffee according to the directions on the coffee maker.
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 (with milk and sugar if desired).