Is called a bechamel sauce or a roux.
Actually, a roux is not a sauce, but is the base for several different sauces and is used as a thickener in many dishes. A roux is made by combining equal parts of fat and starch (usually butter or lard and flour) and cooking it in a pan until the flour taste has been cooked out. The color of a roux depends upon the amount of time you cook it - and the darker the roux, the more flavor it imparts to the dish you are using it in. By adding milk to a roux you are making a bechamel sauce which is used in many lasagna recipes and other dishes. Bechamel sauce is also the base sauce for several other culinary sauces: Mornay sauce (cheese sauce), Mustard sauce, and Sauce Soubise (contains finely chopped onions that are sweated in butter before adding to the sauce) are a few of these.
Roux is basically an emulsive agent -- butter adds the fat.
no
Roux sauce helps thicken anything that it is added to. Watery mushroom soup isn't as appealing as it would be a thick, hearty soup.
Mornay sauce starts out as a bechamel sauce (a basic roux of flour, milk & butter). Then it is added with a cheese, such as gruyere.
Tarragon.
I believe you're referring to a roux.
roux saucecheese saucecream saucebolognese saucetomato saucepesto sauce
veloute
Saute wine in a pan reducing the water out of it to concentrate the flavors.
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