I like preparing a large quantity of Roux and pouring them in ice trays to keep them in the freezer. However, I'm always confused about the right way of defrosting them for use.

The typical use of it is to make white sauce for mac n cheese/pasta. The way i've been using them till now is to take the require amount of milk in a pan, add the cubes and then let it be for 5 minutes or so THEN start the heating. But I'm not convinced this is the best way.