Step 1

Preheat the oven to 425 degrees.

Step 2

Whisk together the flour, baking powder, baking soda, sugar, and salt in a large bowl.

Step 3

Use a box grater to grate the frozen butter and add immediately to the flour mixture. Mix the butter in with your finger tips just until you have coarse meal.

Step 4

Add the buttermilk and stir in until just combined. The dough will be very shaggy.

Step 5

Turn the dough onto a lightly flour surface and press together to form a 10 inch square. Fold in half, then in half again so you have a square.

Step 6

Lightly roll the dough into a 10 inch square again and repeat the folding, in half, then in half again so you have a square.

Step 7

Lightly roll the dough to 1 inch thickness and cut out the biscuits with a 3 inch cookie cutter (round or square). Be sure you don't twist the cutter, just press down and pull up to insure that you get a good rise. Gently gather and reform the scraps to cut the remaining biscuits.

Step 8

Place biscuits in a cast iron skillet or parchment lined baking pan with sides, so the biscuits are touching (they may topple if the baking pan doesn't support them on their sides). Place the pan in the refrigerator or freezer for at least 15 mins.

Step 9

Brush with buttermilk and sprinkle with flaky sea salt. Bake in the middle or upper rack of your oven until risen and golden, about 20-22 mins. Serve warm or at room temperature.