My kids (and I) love snickerdoodles. I have a tried and true recipe, and they taste great. The problem is that once they cool completely, they are hard as rocks. We zap them in the microwave for a few seconds & they are great, but I want to know WHY they get so hard and how to avoid this problem. I store them in ziploc bag (for the short time they last around the house), but they seem to get hard almost immediately. What am I missing?