In a small bowl, whisk together the beer, Worcestershire, onion powder, paprika and salt.
Place the steak in a baking dish, cover with the marinade. Cover and refrigerate for 6 hours and up to 24, turning at least once while marinating.
To make the chimichurri combine all ingredients in a food processor, pulse several times until combined.
Remove the steak from the marinade, pat dry. Allow to sit at room temperature for 15 to 20 minutes.
Preheat the oven to 400.
Pat the steak dry again, if needed, sprinkle on both sides with salt and pepper.
Melt the butter in a cast iron skillet over high heat.
Add the steak, cook for two minutes, flip and cook on the other side for one minute.
Transfer to the oven and cook for 7 minutes or until the thickest part of the steak reads 120 on a meat thermometer.
Remove from the pan and allow to rest for ten minutes. Slice against the grain and serve with the chimichurri sauce