Preheat your oven to 425°F (220°C) and line a baking sheet with a silicone baking mat or parchment paper.
In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.
Add the cold butter slices to the dry ingredients. Use a pastry blender or two knives to cut the butter into the flour mixture until it resembles coarse crumbs.
Create a well in the center of the mixture, then pour the cold buttermilk into the well.
Stir the buttermilk gently into the dry ingredients until just combined. Be careful not to overmix; the dough should be slightly shaggy.
Turn the dough out onto a floured work surface and pat it together into a rectangle.
Fold the rectangle in thirds, then give the dough a half turn. Gather any remaining crumbs, flatten it back into a rectangle, and repeat the folding and pressing process two more times.
Roll the dough on the floured surface until it's about 1/2 inch thick.
Use a 2 1/2-inch round biscuit cutter to cut out biscuits. If you have any dough scraps, reroll them to cut more biscuits. You should get a total of 12 biscuits.
Transfer the cut biscuits to the prepared baking sheet. Use your thumb to make a small indent in the top of each biscuit, which helps them rise evenly.
Brush the tops of the biscuits with a little extra buttermilk.
Bake the biscuits in the preheated oven for approximately 15 minutes, or until they are flaky and golden brown.