In a large bow,l sift together the flour, salt, baking powder, and cinnamon. In a separate bowl, mix the butter and brown sugar. Stir in the eggs, then add the bananas. Stir in the vanilla.
Combine the liquid mixture with the dry ingredients, stirring together only until mixed. Stir in chopped nuts.
Transfer the batter into greased muffin cups, filling 2/3 full.
Bake in a 350°F oven for 25-30 minutes or until a toothpick inserted in a center comes out clean.
Makes 18 to 20 muffins.