Preheat oven to 350°F. Grease an 8.5” x 4.5” loaf pan.
In a bowl, combine flour, baking soda, baking powder, and salt.
In a bowl using an electric mixer, combine butter and Splenda Stevia Sweetener; beat until light and fluffy. Add buttermilk, eggs, molasses, and vanilla extract; beat to combine.
Gradually add dry ingredients and beat until smooth.
Add mashed banana, chocolate chips, and walnuts. Stir just until mixed. Transfer batter to prepared loaf pan.
Bake for 50–60 minutes, until a wooden pick inserted into center of bread comes out clean. Cool in pan about 10 minutes, then remove to a wire rack to cool completely.