I have had this same problem - looking for a yogurt icing recipe that dries hard. A friend told me to use yogurt chips but I had a hard time finding them and when I did, I found they were loaded with sugar! Then I found a product called "Fido's Frosting" on a web site www.k9cakery.com. It says it is what dog bakeries use. I tried some and it was great! It was made with real yogurt, dried hard and was simple to use. I was so excited to find it I wanted to share.

I hope this helps you.