Champignons Sautes au Beurre

In a large, heavy skillet over high heat, heat the butter and oil. As soon as the butter foam begins to subside add the mushrooms. Toss and shake the pan for 4 to 5 minutes. During their saute the mushrooms will at first absorb the fat. In 2 to 3 minutes the fat will reappear on their surface, and the mushrooms will begin to brown. As soon as they have browned lightly, remove from heat. The mushrooms must not be crowded in the pan. If you saute too many at once they will steam rather than fry. If you are preparing a large amount, saute in batches. They may be cooked in advance and set aside. Reheat when needed.