Roux. This is a blend of butter and flour, the basis for countless thousands of sauces. The butter and flour are generally cooked together briefly before a liquid is added, which in turn becomes thickened and smooth to produce a sauce. A roux of butter and flour, worked together until smooth, is called a beurre manié and may be added to boiling sauces, bit by bit, to thicken the sauces.

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