Preheat oven to 350 degrees F.
Grease a 12 cup capacity muffin tin or use paper liners.
With a wooden spoon, mix butter into the mashed bananas in a large mixing bowl. Mix in the sugar, egg, coffee and vanilla. Sprinkle the baking soda and salt over the mixture and mix in. Add the flour, mix until it is just incorporated. Fold in the chopped pecans. Pour mixture into a prepared muffin tin. Bake for 20 to 30 minutes. Cool on a rack.
To check to see if the muffins are done; with a toothpick insert into the center of a muffin, if it comes out clean, it's done.