Add the flour, sugar, salt, baking powder, and baking soda to a food processor and pulse 1-2 times to evenly mix.

Cut the butter into 6-8 pieces and add to the food processor. Pulse 4-5 times until the butter is incorporated and the largest pieces are about the size of a pea.

Remove the food processor's blade or transfer to a bowl and slowly stir in the buttermilk with a fork. Once a scruffy dough has formed (it will look slightly dry), transfer to a work surface. Gently knead the dough and press into a 5.5" to 6" square, about 1" tall.

Cut the dough into 4 pieces and stack them on top of one another, adding any straggling pieces in between layers. Press the dough down and roll into another 1" tall square.

Thinly trim the square's edges before cutting 4 square biscuits. (Discard trimmings or see post above for ways to repurpose.) Transfer to a small sheet pan or plate and freeze the biscuits for 10 minutes.

Place the biscuits in an air fryer basket and brush with a tablespoon of melted butter. Air fry for 10-12 minutes at 375ºF until golden brown on top.