Line a baking sheet with parchment paper. In a large bowl, whisk together flour, sugar, baking powder, salt, and baking soda.
Add cold butter and toss to coat in the flour. Use a pastry cutter or two forks to cut the butter into the flour mixture until the butter is the size of peas. (Alternatively, you can grate the butter into the flour mixture using the large holes on a box grater. Then toss the butter fingers in the flour mixture with your fingers).
Add the buttermilk and stir with a fork just until a shaggy dough comes together. Gradually add a little more buttermilk if the dough is too crumbly. It will be fairly dry (not wet and sticky) but should hold together when pressed and you shouldn't see any dry flour at the bottom.
Turn the dough onto a lightly floured surface. Gently pat into an 8-inch square about 1 inch thick.
Use a bench scraper or large knife to cut the dough into 4 equal squares.
Stack the squares on top of each other. Pat or roll into an 8-inch square again. Repeat two more times (cutting into 4 squares, stacking, and patting into a square).
Use a floured knife or bench scraper to cut the dough into 12 to 16 squares.
Arrange about ½ inch apart on the prepared baking sheet. Freeze for 15 minutes while you preheat the oven to 425°F.
Brush the tops of the biscuits with half of the melted butter.
Bake until golden brown, about 15 to 18 minutes. Brush the hot biscuits with the remaining melted butter.
Serve warm.