If you're going to use the bases immediately they are best stored in the refrigerator until you are ready to top them, otherwise pop them in the freezer until you're ready for them.

Remove bag from the freezer and open carefully using a sharp knife to slowly seperate the two frozen bases. If you are only using one return the other to the freezer. It is best to find some way of sealing the pack before returning it - a snap lock bag if you have one.