This makes correcting the thickness of sauces and gravies nearly fool-proof.

1 stick (1/2 cup) unsalted butter, at room temperature
3/4 cup all-purpose flour

1. Place the butter into a medium size bowl. With a fork, mash in the flour a little at a time until smooth and lump free.
2. Scoop the mixture onto a piece of plastic wrap and form into a log. Wrap tightly and chill.
3. When the log is firm, slice it into 8 equal pieces.
4. To thicken a sauce or gravy, bring the sauce to a safely high temperature and whisk in the Beurre Manie, starting with a one piece and adding more as needed. Stir until thickened.
5. If the sauce has had no previous thickening, you will need about 1 slice per cup of liquid for a moderately thick sauce.