- For best results, use fresh marshmallows.- 1 jar (7 oz.) marshmallow crème can be substituted for marshmallows.- Diet, reduced calorie or tub margarine is not recommended.- Store no more than two days at room temperature in airtight container.- To freeze, place in layers separated by wax paper in airtight container. Freeze for up to 6 weeks. Let stand at room temperature for 15 minutes before serving.