In a large mixing bowl, use a spatula or wooden spoon to mix melted butter into the mashed bananas. Add the sugar, egg and vanilla, then add the spices. Sprinkle the baking soda and salt over the mixture and mix in. Add the flour last; mix.
Pour mixture into a buttered 4 x 8-inch loaf pan. Bake for 50 minutes to 1 hour, or until a tester comes out clean. Cool on a rack. Remove loaf from pan and slice to serve.