Set the Sous Vide cooker with a water bath at 137 degrees.
Heat the olive oil in a cast iron skillet on medium-high.
Sprinkle the beef tenderloin with salt and pepper.
Sear the tenderloin in the skillet, turning until it is nicely brown on all sides.
Put the parsley and garlic in a ziploc or sous vide bag and add the tenderloin. Seal the bag.
Add the bag to the water that is heated by the sous vide cooker and let it cook for 2-3 hours.
Once the tenderloin has cooked about 2 hours heat the remaining olive oil in the skillet.
Add the mushrooms and cook for 5-10 minutes, until browned. Remove the vegetables to a small bowl.
Remove the tenderloin from the bag, but reserve any juices that are in the bag. Sear the tenderloin in the skillet for 2 minutes, rotating to brown on all side.
Remove the tenderloin to a plate to rest.
Return the mushrooms to the skillet and stir in the flour. Pour in the juices left in the sous vide bag and add the beef broth.
Cook, stirring, for 3-5 minutes until the sauce thickens.
Slice the beef tenderloin and serve with the mushroom gravy.