Mix together all ingredients in a medium bowl. Stir well and let sit for at least 30 minutes up to overnight.
Make the Rib Eye Steaks
Generously season steaks on both sides with rosemary, garlic, salt, and pepper.
Heat butter in a large cast iron skillet (or other heavy skillet) over medium heat.
Add steaks to the hot pan. If they are too large to cook both in one skillet, cook in batches; you want to be sure each steak has room around it to cook evenly. Cook until you see the bottom turning brown, about for 4-5 minutes, before flipping over to cook the other side. Spoon butter from the pan over each side as it cooks.
Once steaks are cooked to your liking, remove steaks from skillet and allow to rest on a carving board/plate for at least 10 minutes. Serve with chimichurri sauce spooned over the sliced steaks.
Notes
Cast iron tip: To keep the steak from sticking to the cast iron pan, add a teaspoon of oil to your skillet before you start cooking. Then slowly warm up the pan until you reach cooking heat.