Dump the jar of biscuit mix in a mixing bowl and cut in the cold butter using a pastry cutter or fork. Add your buttermilk and stir with a large spoon until all the dough starts to stick together.
Dump biscuit dough onto a lightly floured surface and fold it over a few times with your hands, being careful not to handle it too much (you don’t want the cold butter to melt, so don’t overhand the dough). Pat dough out into a thick disc, about 1 to 1½ inches thick.
Cut out your biscuits with a biscuit cutter and place on a baking sheet. Bake for about 15 minutes.
Notes
If you don’t have buttermilk on hand, you can make your own by combining one cup of full-fat milk or cream with one tablespoon of lemon juice or white vinegar. Let sit for about five minutes and it will curdle and be ready to add to the rest of the ingredients! (I use this in place of real buttermilk all the time and it works great!)
No milk? You can use plain yogurt in place of the buttermilk.