Muffins can turn out hard if the ratio of wet ingredients to dry isn’t correct. This can happen if the flour has been measured incorrectly. The right way to measure flour is to first stir the flour to lighten it and then spoon the flour into the measuring cup without packing it in. An even more accurate way is to weigh the flour. Another reason that your muffins turn out hard is if they’ve been overcooked. Ovens vary greatly. The more you use your oven, the better you’ll be able to judge when muffins are ready. Muffins will be well risen, browned and look dry on top when cooked.