Filet mignon, or beef tenderloin, is a super tender, lean cut of beef that is often served as a fancy steak. Filet is so lean it lacks a lot of the flavor of fattier cuts so it is often complemented with a strongly flavored sauce. For this recipe I turn to a creamy blue cheese sauce and some sherried mushrooms to round out the flavors of the meal. I also cook it with Worcester sauce for added flavor.
Filet mignon is one of the best steaks to cook with sous vide because any overcooking starts to turn the filet chewy. It's the most tender cut of beef and it only needs to be heated through the sous vide process, not tenderized. You can either measure the thickness and cook it for the minimum time needed or just give it 2 to 3 hours. This recipe works just as well for a tenderloin roast as it does for steaks, just increase the time in step with the bigger width of the tenderloin.
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Preheat a water bath to 131°F (55°C).
Salt and pepper the steak then sprinkle with the garlic powder. Place the steak in a sous vide bag, add the Worcester sauce, then seal. Cook the filet mignon until heated through, about an hour for a 1" (25mm) steak or 3 hours for a 2" (50mm) steak.
Blend all of the ingredients together until smooth. The cheese sauce can be stored in the refrigerator for a day or two.
Clean and de-stem the mushrooms then cut into large pieces. Heat the oil over medium heat then add the onion and garlic. Cook until the onion is translucent, about 10 minutes. Add the mushrooms and rosemary then cook, stirring occasionally, until the mushrooms are tender. Add the sherry and cook until the sherry has evaporated. Stir in the butter until it melts. Remove from the heat and stir in the lemon juice.
Lightly salt the outside of the filet mignon then quickly sear it until the meat is just browned.
Place the filet mignon on a plate with the sherried mushrooms. Top the steak with the blue cheese sauce then sprinkle some rosemary leaves on top.
For an upscale modernist take you can turn the blue cheese sauce into a thick foam using a whipping siphon. Omit the olive oil and increase the heavy cream to 3/4 cup. Blend everything together then pour it into a whipping siphon. Seal and charge the siphon then dispense onto the steaks. The blue cheese foam can be made a day or two ahead of time and stored in the refrigerator.