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1
In each of 2 large skillets, melt 1 1/2 tablespoons of the butter.
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2
Add the onion to one skillet and the mushrooms to the other.
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3
Season both with salt and pepper and cook over high heat until the onion is softened and the mushrooms are browned and tender, about 5 minutes.
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4
Off the heat, add the Cognac to the mushrooms.
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5
Cook over high heat until evaporated, about 10 seconds.
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6
Add the mushrooms to the onion and wipe out the skillet.
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7
Add the stock to the mushrooms and boil until nearly evaporated, 5 minutes.
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8
Stir in the creme fraiche and mustard and simmer until thickened, about 5 minutes; keep warm.
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9
In the empty skillet, melt the remaining 1 tablespoon of butter in the oil.
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10
Season the meat with salt and pepper and add it to the hot skillet.
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11
Cook over high heat, turning once, until lightly browned in spots but still rare, about 2 minutes.
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12
Scrape the meat and any juices into the mushroom sauce and simmer just until heated through, 1 minute.
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13
Serve right away, with the rice pilaf.
