General Cooking Questions

I have a problem that I need some resolution with.
I am making a potatoes au gratin recipe that calls for making a blonde roux and allowing it to cool to room temperature, and then add the blonde roux into a boiling chicken stock (tones chicken base + water), after which heavy cream is added to cut the stock down a bit. The consistency is sort of a thicker napé that congelates upon refrigeration (this helps to keep the layers of potatoes together and the au gratin potatoes can then be cut into squares and served).