Chill a large mixing bowl, pastry cutter, the flour and 1 stick butter in the freezer for 15 minutes before assembling the biscuits.
Preheat the oven to 425 degrees F. Place a cast-iron skillet in the oven to preheat.
Add the chilled flour to the chilled mixing bowl. Working quickly, cut the chilled butter into the flour using the chilled pastry cutter (or your fingers); the goal here is pea-size clumps of butter. In batches, add the buttermilk, mixing, until the dough is cohesive yet still moist.
Turn the dough out onto a floured surface and lightly press into a 1-inch-thick round. Using a biscuit cutter or the business end of a dry measuring cup, cut out 8 biscuits.
Carefully remove the skillet from the oven and add the oil. Place the dough rounds into the hot skillet right up against each other and brush with the melted butter. Bake until golden brown, about 15 minutes.