Preheat oven to 425°F/218°C. Line a baking sheet with parchment paper.
Place flour, sugar, baking powder, baking soda, and salt in a food processor or in a large bowl. Pulse in the food processor or whisk in a bowl until ingredients combine. Add cold butter cubes, and cut into the flour mixture by pulsing a food processor or using a pastry cutter until mixture resembles coarse crumbs. Transfer the mixture into a large bowl if you use a food processor before mixing with cold buttermilk.
Add buttermilk to the bowl and stir by hand until a sticky dough is formed. Don’t overmix.
Turn out dough onto a floured-surface and quickly form into a rough square. Pat the dough into a 3/4-inch-thick rectangle. Fold the dough in thirds (like folding a letter), then lightly pat the dough back out into another 3/4-inch rectangle. Repeat the process three more times, making sure to to work the dough as quickly and lightly as possible so the dough will stay cold during the work. You may need to put the dough back in the fridge at some point to keep the butter cold when you feel the dough gets warmer or butter starts to melt.
Roll your dough with a rolling pin until it’s about 3/4 - 1 inch thick. Use a round cookie cutter (or biscuit cutter) firmly press down straight into the dough, don't twist the cutter. Place biscuits on the prepared baking sheet. You can gather all the scraps and reroll and cut until you get around 10-12 biscuits.
Brush the tops lightly with buttermilk and bake them at 425°F for 13-15 minutes until risen and golden brown.
Serve with any filling you like, from butter to jam, nutella or any kind of spread. Leftovers can be frozen for up to 2 months. Reheat in the oven before serving.