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1
Fill a large Dutch oven about 2/3 full with water. Bring water to 130 degrees F (54 degrees C) over medium heat. Attach a candy/oil thermometer to the side of the Dutch oven in order to monitor and maintain the water temperature.
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2
Generously season steaks with salt and black pepper. Heat vegetable oil in a large skillet over high heat. Place steaks in skillet and cook until just browned, 1 minute per side. Transfer steaks to a resealable plastic bag, squeeze out all air, and seal.
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3
Place plastic bag containing steaks in the Dutch oven, adjusting the heat as necessary to maintain the temperature at 130 degrees F (54 degrees C). Cook for 2 1/2 hours, moving the bag around occasionally and maintaining the temperature.
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4
While the steaks are cooking, heat 1 tablespoon butter in the skillet over medium-low heat. Add mushrooms; cook, stirring, until mushrooms are soft, 5 minutes. Transfer to a plate and set aside.
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5
Remove steaks from plastic bag (reserving any accumulated juices) and pat dry. Generously season with salt and pepper. Heat 1 teaspoon vegetable oil in the skillet over high heat. Place steaks in skillet and cook to form a crust, 2 minutes per side. Transfer steaks to a plate.
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6
Stir garlic and reserved mushrooms into skillet, reduce heat to medium, and cook until mushrooms are reheated, 2 minutes. Stir in reserved juices, water, and balsamic vinegar. Remove from heat.
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7
Stir in 1 tablespoon cold butter until completely melted and incorporated. Season with salt and pepper to taste. Spoon sauce over steaks and serve.
