Preheat the oven to 350°F (180°C). In a large bowl, mix together the flour, sugar, baking powder, baking soda, and salt.
Cut in the cold butter with a pastry blender or fork until it resembles small crumbs. Add the buttermilk and orange zest. Mix until a soft dough forms.
Dust a surface with some flour and knead the dough gently for a few seconds. Roll out the dough into 1-inch thick circles. Cut 3-inch rounds from the dough and transfer them to an ungreased baking sheet.
Brush melted butter over the top of the bisconie and then sprinkle with turbinado sugar. Bake for 13-15 minutes or until golden brown.
Serve warm with ice cream, whipped cream, or just as it is.