Both use the same ratio of 1 part flour to 1 part butter. And each one is used to thicken sauces like gravy, soups, and stews. The main difference is roux is cooked first in a pan, using melted butter and flour, whisking over lower heat which turns it a darker color. A beurre manié is made by mashing uncooked soft butter with flour into a paste on a plate or in a bowl with a fork and then adding the mixture to the recipe during the cooking process.