Chill tools: place a large mixing bowl, box grater, biscuit cutter, flour, and butter in the freezer for 15 minutes.

Preheat oven: set oven to 425°F (220°C) and put a large cast-iron skillet in the oven to heat.

Combine flour and butter: in the chilled bowl, add 4 cups self-rising flour and grate the frozen butter into the flour. Stir until butter is evenly distributed.

Add milk: pour in 2 cups cold milk or buttermilk and stir gently until the dough just holds together, adding more milk if necessary to achieve a lumpy and slightly tacky consistency.

Shape and layer: turn the dough onto a lightly floured surface, press out to about 3/4-inch thick, fold the dough in half, press out, and repeat to create layers.

Final roll and cut: roll or press back to 3/4-inch thickness and cut 8–10 biscuits using a large biscuit cutter.

Heat the skillet: carefully remove the hot cast iron from the oven, add 1 tbsp oil, and swirl to coat. Arrange biscuits in the skillet.

Brush and bake: brush tops with melted butter and bake for 15 minutes or until deep golden brown.

Serve warm: remove from oven, brush again with melted butter, and serve.