In a large mixing bowl combine flour, baking powder, sugar and salt until blended.
Using a grater, grate the butter and stir into the flour mixture. This ensures that the butter mixes well with the dry ingredients.
Add milk and buttermilk and stir until a dough forms.
Generously flour a flat surface and turn the biscuit dough out onto the floured surface.
Using your hands press the dough into a rectangle.
Fold the dough in half and, using a 2 1/2-inch round biscuit cutter, cut ithe dough nto 12 biscuits, rerolling if necessary.
Set the air fryer temperature to 390F.
Arrange biscuits in the air fryer basket in a single layer and, if desired, brush tops with melted butter.
Depending on the size of your air fryer you may need to air fry the biscuits in two batches.
Cook for 9 minutes or until golden and baked through.