Beurre manié is a paste made from flour and softened butter. It’s used to thicken gravy and stews
-Press together equal quantities of butter and flour in a small bowl, using your hands.
-Add a little of the beurre manié to the pan and whisk well.
-Continue to whisk until the sauce has the desired consistency, adding more beurre manié if necessary.
Source: https://www.bbc.co.uk