Step 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.
Step 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.
Step 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.
Step 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.
Step 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.
Step 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.
Step 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.