Finely chop 1 large onion and sweat it in butter without letting it brown. When the onion is completely cooked, sprinkle over 2 tablespoons (30 milliliters) of paprika. Add 1 quart (1 liter) of sauce velouté to the mixture and gently simmer the sauce for 10 to 15 minutes. Thin the sauce to the desired consistency with white stock, milk, heavy cream, or a mixture. Strain the sauce through a fine chinois and finish it by whisking in 4 ounces (125 grams) of butter.