The onion sauce I made at the weekend was not a success.
My theory had been that cooking the onion in milk first, rather than in water, would produce a more flavoursome sauce. But the reduced and grainy milk gave the dish a rather sickly quality.
I roughly chopped two onions, covered them in milk seasoned with salt and nutmeg, and simmered them for 25 minutes. I made a roux with a dstsp of flour and enough butter (about 20g, I should guess) to turn it into the consistency of wet sand; I cooked the roux very gently for two minutes, and poured in the milk and onions gradually, incorporating each addition before pouring in the next.
In Nigella Lawson's How To Eat, the recipe advises cooking the onions -- cut however you like them -- in water. You retain the water when you drain them, and make a sauce with that and an equal quantity of flavoured milk; then you add onions and cream.
Or there is Nigel Slater's baked onions, from Kitchen Diaries. You peel the onions, simmer them for 20 minutes, cut them in half and place in a baking dish, pour over cream and scatter with parmesan. Bake until bubbling.
I am sure that both recipes are nicer than mine.