Set your oven to 450°F (230°C) and let it fully preheat. Line a rimmed baking sheet with parchment paper and place your butter cubes in the freezer for 10 minutes if your kitchen is warm.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, sugar, and salt for a full 20 to 30 seconds to make sure the leaveners are evenly distributed.
Add the cold, cubed butter to the flour mixture. Using a pastry cutter, two forks, or your fingertips, work the butter into the flour until the mixture looks like coarse crumbs with some pea-sized pieces of butter still visible. Alternatively, grate the frozen butter directly into the flour using a box grater and toss gently to coat.
Make a well in the center of the flour and butter mixture. Pour in the cold buttermilk all at once and stir gently with a fork or spatula just until a shaggy, slightly wet dough forms. Stop as soon as you no longer see dry patches of flour.
Turn the shaggy dough out onto a lightly floured surface. Pat it into a rough rectangle about 1 inch thick, fold the dough in half, then pat it back out again. Repeat this folding process 3 to 4 times.
After the final fold, pat the dough into a rectangle about 1 inch thick. Dip your biscuit cutter in flour, then press straight down through the dough without twisting. Gather the scraps, gently pat together, and cut a few more biscuits.
Place the biscuits on the prepared baking sheet so their sides are touching. Brush the tops lightly with the melted butter or a splash of extra buttermilk.
Bake in the preheated oven for 12 to 15 minutes, until the tops are golden brown and the biscuits have risen tall. Rotate the pan halfway through baking if your oven has hot spots.
Remove the biscuits from the oven and brush the tops with a little more melted butter while they are still hot. Let them rest on the pan for 2 to 3 minutes before transferring to a wire rack or serving basket.