Soubise Sauce is a white sauce in classical French cooking that is mildly onion-flavoured.
It can be used on grilled meat or fish, or served with poultry dishes.
It is based on Béchamel sauce (aka White Sauce.)
Put 1/4 cup (2 oz / 50g) of finely chopped onion in a heat-proof bowl; add some water, and zap in microwave until the onion is softened, making sure the water doesn't boil away on you to dry out or brown the onion (the onion must not brown.) Drain.
Add to béchamel sauce, along with a tablespoon or two of cream. Stir, adjust seasoning to taste. To serve, reheat, then strain out and discard the onion.
Literature & Lore
483. Ingredients - 1/2 pint of Béchamel, No. 367, 1 bay-leaf, seasoning to taste of pounded mace and cayenne, 6 onions, a small piece of ham.
Mode - Peel the onions and cut them in halves; put them in a stewpan, with just sufficient water to cover them, and add the bay-leaf, ham, cayenne, and mace; be careful to keep the lid closely shut, and simmer them until tender. Take them out and drain thoroughly; rub them through a tammy or sieve (an old one does for the purpose) with a wooden spoon, and put them to 1/2 pint of Béchamel; keep stirring over the fire until it boils, when serve. If it should require any more seasoning, add it to taste. Time - 3/4 hour to boil the onions. Average cost, 10d. for this quantity. Sufficient for a moderate-sized dish."
-- Mrs Beeton. 1861.
2 cups sliced onions
1/2 cup cream or milk
1 cup Velouté Sauce
Salt and pepper
"Cover onions with boiling water, cook five minutes, drain, again cover with boiling water, and cook until soft; drain, and rub through a sieve. Add to sauce with cream. Season with salt and pepper. Serve with mutton, pork chops, or hard boiled eggs."
-- Fannie Merritt Farmer. The Boston Cooking-School Cook Book. Boston: Little, Brown, 1918. Fish and Meat Sauces section.