Use very cold or frozen butter. Also, make sure your whey (or buttermilk) is well-chilled. Some people go so far as chilling the flour and their mixing bowl. Chilling the dough for 30 minutes before you cut it into biscuits helps, too. The temperature difference between the biscuit ingredients and the oven causes a pop of steam that helps the biscuits rise high. Make sure your oven is hot, and the biscuit dough is cold!