Cover a pan of uncut brownies and bars with foil – or put the pan in a large resealable plastic bag. (If made with perishable ingredients, like cream cheese, they should be covered and refrigerated.) Once the bars are cut, store them in an airtight container.Most bars and brownies freeze well for up to 3 months. To freeze a pan of uncut bars, place in an airtight container or resealable plastic bag. Or wrap individual bars in plastic wrap and stack in an airtight container. Thaw at room temperature before serving.