Preheat your oven to 400°F (200°C).
In a large mixing bowl, combine the flour, sugar, baking powder, and salt.
Cut in the cold butter until the mixture resembles coarse crumbs.
In another bowl, whisk together the egg, mashed banana, and milk.
Add the wet ingredients to the dry ingredients and stir until just combined.
Fold in the chopped nuts.
Turn the dough out onto a floured surface and knead gently a few times.
Pat the dough into a circle about 1 inch thick and cut into 8 wedges.
Place the wedges on a baking sheet and bake for 15-20 minutes, or until golden brown.