The key to soft sugar cookies is to not overbake them! It's tricky with this recipe since the cookies are dark brown and you can't see when they start to brown. For ¼-inch thick cookies, they're done when the tops appear dry and set. For ½-inch thick cookies, bake for 1-2 minutes more. Baking time will vary greatly depending on the shape of the cookies, so keep a close eye, and bake a small test batch to help you figure it out.