Instructions

• Preheat the oven to 450°F (232°C). Grease a 12-inch deep-dish cast-iron skillet and set it aside.
• Sift the 4 1/2 cups all-purpose flour. Place the sifted flour, 1/4 cup granulated sugar, 2 tablespoons baking powder, 1 teaspoon baking soda, and 2 1/2 teaspoons sea salt in a food processor. Pulse 3–5 times to combine the dry ingredients.
• Cut the 1/3 cup cold butter-flavored vegetable shortening and the 1/4 cup cold butter (half of the 1/2 cup butter) into small pieces if needed. Add them to the food processor. Pulse in 8–12 short bursts, until the mixture resembles coarse pebbles and the fats are evenly distributed. Work quickly so the fats stay cold.
• With the processor running in short pulses, add the 2 cups cold buttermilk a little at a time (pouring slowly or in 2–3 additions). Pulse just until the dough comes together and looks wet but even—do not overmix. Stop pulsing when there are no large dry patches of flour.
• Dump the dough onto a lightly floured work surface. Gently press and pat the dough into an even 2-inch-thick disk. Handle the dough as little as possible.
• Using a 3-inch biscuit cutter or a drinking glass, cut out 8 biscuits. If needed, cut 7 biscuits first, then gather the scraps, press gently to 2 inches thick again, and cut the final biscuit. Avoid twisting the cutter when cutting.
• Arrange the biscuits in the prepared skillet so they sit next to each other. Brush the tops of the biscuits with the remaining 1/4 cup melted butter (the other half of the 1/2 cup butter).
• Place the skillet on the center oven rack (move racks as needed to allow at least 1–2 inches of clearance above the skillet). Bake 30–35 minutes, until the tops are golden and the biscuits have risen at least 1 inch above the rim of the skillet.
• Remove the skillet from the oven. Use a spatula or a knife to separate the biscuits, then lift them out of the pan. Serve warm.