First, make the chimichurri by placing the herbs and garlic into a food processor (or blender). Add the vinegar, red pepper flakes, salt and black pepper to taste.
Pulse it a few times then continue pulsing while adding 3/4 cup of the olive oil. Keep pulsing until the mixture is pulverized, leaving just a little texture from the herbs. Transfer to a bowl, then cover and refrigerate until you need it (you can make it up to 1 day ahead, though it's best to make it the same day).
Season the steak on both sides with salt and pepper. Heat a cast-iron skillet over medium-high heat and add the butter and remaining 2 tablespoons olive oil. When it's melted and starting to brown, add a steak. Fry until medium rare, 3 to 4 minutes per side. Remove the steak and let it rest for 3 minutes. (If you're frying more steaks, just add a little more butter and oil to the pan as needed.)
Slice the steak. Serve it with the chimichurri on the side.
"The Pioneer Woman Cooks: Come and Get it! Simple, Scrumptious Recipes for Crazy Busy Lives" by Ree Drummond © William Murrow 2017. Provided courtesy of Ree Drummond. All rights reserved.