Yes! It's a nifty trick, and best recommended for white or blonde roux. Simply cook a large amount and then let it cool off heat. When cool enough to handle, pour it into an airtight container and store it in the fridge for up to 6 months, or longer in the freezer. When you're ready to use it, start with 1-2 tablespoons to thicken a sauce. You'll need to let frozen roux thaw first. Keep in mind that the hot roux + cool liquid rule applies in reverse: only add refrigerated roux to a hot liquid.