When biscuits turn out hard and cracked instead of tender and flaky, one of two culprits is usually responsible: overworked dough or low oven temperature. Biscuit dough should be handled as little as possible with the right utensils prior to baking. Biscuits also require high heat to bake properly. Check your oven temperature to ensure it's heating correctly before baking your biscuits.
Whisk It Together
To make biscuits, combine flour with baking powder or baking soda, sugar, salt, butter, egg and milk. Instead of using a stand-up or hand mixer, place the dry ingredients in a bowl and stir them with a wire whisk to combine your flour with the baking powder and salt. Whisk the dry ingredients together just long enough to incorporate the baking powder thoroughly into the flour.
Cut It Correctly
Cut the butter into several pieces and add the pieces to the dry ingredients. Use a pastry cutter to "chop" the butter into the dry mixture. If you don't have a pastry cutter, use two butter knives instead. Take a knife in each hand and "cut" the ingredients using a crosswise motion. Cut the butter just until it resembles coarse, flour-coated crumbs.
A Light Hand
Once the butter and dry ingredients are combined, add egg and milk and form the mixture into a dough ball. Roll the ball all around the bowl to gather up the flour, but don't work the dough any more than is needed to combine the ingredients. Place the ball on a floured surface and either roll it out with a rolling pin or flatten it with your hand to 1/2-inch thickness. You can use a round cookie cutter or even the top of a drinking glass with the preferred circumference to cut out the biscuits. Place the biscuits on a baking sheet prepared with a cooking spray or a parchment sheet.
High Heat
Bake biscuits at 400 degrees Fahrenheit for 10 to 15 minutes until golden brown. They're done when a toothpick inserted into the center of one comes out clean. Cool the biscuits on a wire rack. Leave them uncovered for crusty biscuits, or wrap them in a clean dish towel to cool for softer crust. The biscuits' insides should be soft, light and white.
Check the Temperature
If a slow oven seems to be the cause of tough biscuits, it's as easy as boiling water to check the oven temperature to ensure the elements are heating correctly and that your thermostat is correct. Place an ovenproof bowl half-filled with water on a middle rack in the oven. Since water boils at 212 degrees Fahrenheit, set the oven temperature for 210 F. If the water doesn't boil, then the oven is "cold." If the water boils, then it's "hot." Alternatively, hang an oven thermometer on a rack in the oven and check it using the oven light when heated to a predetermined temperature. If it's not heating correctly, you have three options: adjust the cooking temperature to compensate for the oven temperature, consult the owner's manual to change the temperature setting, or have a repair service calibrate the oven.