Pluck off parsley leaves from the stem. Add parsley, chopped garlic, olive oil, red wine vinegar and red pepper flakes in food processor or blender. Blend until the ingredients are finely chopped. Salt and pepper to taste.
Set aside 1 to 2 hours to emulsify flavors.
Set sous vide machine to 54C/129F.
Salt and pepper the steak. Put the steak in a freezer bag, and remove the air through a vacuum sealer or the displacement method. Place steak in the bath. Cook for 1 -2 hours.
Remove steak from bath. Pat dry with paper towels. Heat pan on high and add oil. Sear for 60-90 seconds on each side. Remove from pan and let rest for 5 minutes
Serve steak topped with chimichurri sauce and enjoy!