Preheat the oven to 375F (190C).
Add the turmeric to a pot of boiling, salted water.
Add the potatoes and simmer, covered, for 4 minutes.
Put the oil in a roasting pan and put it in the oven for 5 minutes to heat up.
Drain the par-cooked potatoes and shake them to roughen the surfaces (just a little, not too much) because this helps them crisp.
Tip the potatoes into the hot oil, then toss with a metal spoon.
Sprinkle with paprika (and a little cayenne if liked).
Roast for 1 1/4 hours without turning them, or until crisp and golden brown.
Sprinkle salt over them (maybe some black pepper too if liked).
Serve hot with some sour cream and/or cheese on top.
