Preheat the oven to 425°F (220°C) and line a large baking sheet with parchment paper.
In a large bowl, whisk together the flour, baking powder, and salt. Add the cold, cubed butter and use a pastry cutter to cut the butter into the flour until pea sized lumps form.
Add 250 ml (1 cup) of buttermilk to the flour and use a silicone spatula to mix and fold everything together until a shaggy dough forms.
Tip the dough out onto a lightly floured surface and with floured hands, quickly bring the dough together into a cohesive ball.
Sprinkle the top of the dough with a little flour and use a rolling pin to flatten it into a ¾-inch (2 cm) thick horizontal slab.
Fold one of the short ends into the center of the dough then fold the other on top. Turn to orient the dough horizontally again and roll back into a ¾-inch (2 cm) thick slab. Repeat the folding process once more, working quickly so as to not melt the butter. If the dough starts to get sticky, sprinkle a touch of flour on top.
Flatten the dough once more into a ¾-inch (2 cm) thick slab then use a 3-inch (7.6 cm) biscuit cutter to cut out the biscuits (press down, don't twist). Re-roll and cut any leftover dough until you get at least 6 biscuits.
Spread the biscuits out onto the prepared baking sheet and brush with 1 ½ tbsp of buttermilk. Bake for 26-29 minutes until deeply golden brown and fluffy.
Remove the biscuits from the oven and immediately brush with the melted butter.