With a large whisk, mix melted butter into the mashed bananas in a large mixing bowl. Mix in the Nectresse sweetener, egg, and vanilla.
Sprinkle the baking soda and salt over the mixture and mix in. Add the flour last, mixing just until combined. Fold in the chopped walnuts and pour the mixture into a buttered and floured 4x8 inch loaf pan.
Bake for 45-60 minutes, or until a skewer or toothpick inserted into the center of the loaf comes out clean. Cool in the pan on a wire rack. Remove from the pan and slice to serve.
Notes
Per the product packaging, 1 packet of Nectresse = 2 teaspoons of real sugar