I don't know whether I commented on this already as I'm too lazy to read all the comments but there's a very odd peculiarity in this recipe.
Five potatoes are added and cooked for 15 minutes but they are then removed and never added back!
The claim is that they add more flavour, which I am very doubtful of. What's more likely, in my opinion, is that they are just precooking the potatoes in the early stage of making the base sauce for use in other dishes. I'd be willing to bet good money that the cooking of potatoes has no effect whatsoever on the base flavour. They might add some starch to thicken but there are easier ways to thicken the sauce without using a whole bunch of potatoes.
Very odd.