The pieces of butter in the dough were too big. After you cut the fat into the biscuit dough, no pieces should be over the size of a pea. Hint: If you notice smoke leaking out of your oven (burning butter) or see butter dripping from the cookie sheet while your biscuits are baking, do this. Grab another cookie sheet and cover it with a silicone baking sheet, parchment paper, or foil. Slide it onto a rack beneath the biscuits to catch the drips. It is easier to throw away parchment paper or foil than to clean your oven. Also, the drips won't burn and smoke on the cookie sheet as they do on the bottom of your oven. I've already tested this for you. p.s. I always do this when baking pie crusts, too.