Freezing a roux is actually an ideal way to store it so you can always have some on hand to use when you need it. The best way to freeze it is to make individual portions (like in ice cube trays). Place the small portions on parchment paper or waxed paper then stick them in an airtight container or sealable plastic bag before putting them into the freezer. To thaw it quickly, transfer the frozen pieces to your refrigerator a few hours prior to use.  Rouxs can be frozen if stored properly for up to 6 months in the freezer.