Preheat your oven to 450°F (232°C) and line a large baking sheet with parchment paper.

In a large mixing bowl, whisk together 2.5 cups of chilled all-purpose flour, 1 tablespoon of baking powder, 0.5 teaspoon of baking soda, and 1 teaspoon of fine sea salt.

Add 0.5 cup of grated cold unsalted butter to the dry ingredients and toss gently with a fork until coated and crumbly.

Pour 1 cup of cold whole buttermilk into the center and stir with a wooden spoon until a shaggy dough just comes together.

Turn the dough onto a lightly floured surface and pat into a 1/2-inch thick rectangle.

Fold the dough into thirds like a letter, rotate 90 degrees, and pat down again; repeat this folding process 4 times to create flaky layers.

Pat the dough into a 3/4-inch thick rectangle and cut out biscuits using a 2.5-inch round cutter pressed straight down without twisting.

Arrange the biscuits on the prepared baking sheet so their edges lightly touch each other.

Bake at 450°F for 12 to 14 minutes until the tops are golden brown and puffed tall.

Brush the tops immediately with 2 tablespoons of melted unsalted butter and serve warm.