Preheat oven to 425°F and adjust oven rack to middle position. Line a large, rimmed baking sheet with parchment paper. Set aside.
Cut 2 sticks (1 cup) of butter into ½-inch pieces; set aside in the refrigerator.
1¼ cups unsalted butter
Add the flour, baking powder, salt, sugar, and baking soda to the bowl of a food processor. Pulse the flour mixture for 2 seconds (just to incorporate).
3½ cups all-purpose flour, 2½ teaspoons baking powder, 2 teaspoons kosher salt, 2 teaspoons granulated sugar, ¼ teaspoon baking soda
Add the cold cut butter pieces (1 cup) to the flour mixture and pulse until the largest butter pieces are pea size.
Pour the flour/butter mixture into a large bowl. Slowly drizzle the cold buttermilk over the top while continuously tossing the mixture with a fork to incorporate.
1 cup buttermilk
Lightly knead the mixture just a few times until shaggy dough forms (the dough will look dry). Transfer the dough to a lightly floured work surface and gently pat into a 1-inch thick square.
Cut the square into 4 equal sections and stack the 4 sections together. Press the dough into a 1-inch thick rectangle and trim a very thin border around the sides of the rectangle. This will create the clean edges needed to see the layers.
Cut the dough into 12 equal squares (think of a 4x3-inch grid).
Place the biscuits, 2-inches apart, onto the prepared baking sheet. Freeze the biscuits 10-15 minutes.
While the biscuits are in the freezer, melt the remaining ¼ cup of butter.
Brush the biscuit tops with melted butter, garnish with sea salt (if desired), and place in the oven.
Flake sea salt
Reduce the temperature to 400°F and bake 20-22 minutes, or until golden brown and the internal temperature of a middle biscuit reaches 205-208°F.
Transfer cooked biscuits to a cooling rack and serve immediately.