Make the Chimichurri Spice Mix: Combine ingredients (dried oregano through coriander). I like to put them in a glass jar with a lid and shake them together to combine. You'll only need half of the spice blend for the London Broil recipe, so you'll have some leftover for another day.

Make the Marinade: Place ⅓ cup Chimichurri Spice Mix in a large food storage container and pour hot water on top. Mix together and let soak for 5 minutes. Whisk in vinegar and oil, then add the London Broil, flipping it to coat it in the marinade. Cover the container and transfer to the refrigerator. Marinate for 6 hours, shaking the container or flipping the meat over halfway through if possible.

Make the Sauce: Stir together ingredients (yogurt through white wine vinegar) in a small bowl. Cover and refrigerate until ready to use.

Cook the Steak: Preheat oven to 275°F. Place a cooking rack on top of a baking sheet. Remove the London broil from the marinade and place on top of the cooking rack. Bake in preheated oven for 50-60 minutes, or until the internal temperature of the meat reaches 129°F (this is for medium-rare, feel free to cook it for more/less time depending on your desired degree of doneness).

Sear the Steak: Heat 2 tablespoons oil in a large skillet, preferably cast iron, over medium-high heat. When smoking hot, place the steak in the pan, topped with 1 tablespoon butter, and sear the steak for 1-2 minutes per side. Remove from the pan and let rest 10 minutes before slicing thinly against the grain.

Serve sliced steak with sauce alongside for dipping.