Heat the oven to 450°F and line a baking sheet with parchment.
Whisk the flour, baking powder, baking soda and salt, then cut in the shortening until flat pea-size pieces remain.
Stir in the buttermilk just until a shaggy dough forms and turn it onto a lightly floured surface.
Pat the dough 1 inch thick, fold it in thirds, rotate, and repeat the fold twice more.
Pat it 1 inch thick again, cut 10 biscuits with a 2 1/2-inch cutter without twisting, and place them close together on the sheet.
Bake for 12 to 14 minutes until tall and golden, then brush with the melted butter.