Hello! I'm hoping someone can help me! I make these delicious oatmeal cream pies with a vegan vanilla filling. (Made with palm oil shortening, organic powdered sugar, vanilla and almond  milk). It tastes amazing, but the only problem is that after a few hours, the parts of the frosting that you can see between the cookies gets hard.

This is so strange to me, because I am using the same frosting recipe that I top my cupcakes with, and as long as I keep it in an airtight container, it never gets hard like this. The cookies are kept in an airtight container as well…the cookies themselves stay super soft and moist, but the frosting gets rock hard on the outside edges (while staying somewhat soft and creamy on the inside.)

Any suggestions? Cut back on the amount of powdered sugar? I am selling these in little self-sealing cello bags, and don't want them to dry out on the customers who don't eat them right away.

See this:http://cakecentral.com/t/654475/what-makes-a-buttercream-crusting-or-not

Deb says it's the sugar to fat ratio, the more sugar you have the better it crusts. So maybe try using a bit less sugar? I don't know the ratio, but it may say in that thread.

AThank you!!!!!