Mix together flour, Truvia, baking powder and salt.
Cut cold butter into slices and add to flour mixture.
Cut butter into flour mixture with a pastry blender or two knives.
Mix in mashed bananas, buttermilk, egg, vanilla and walnuts with a fork until mixture comes together. Do not over mix or scones will be rock hard. Dough is very wet and sticky.
Divide dough in half and gently form into two 8 inch circles on a greased cookie sheet.
Cut into 8 wedges with a long, sharp, floured knife but do not separate the wedges.
Bake at 425°F for 14 to 16 minutes until golden brown.