Remove steaks from refrigerator 60 minutes before cooking to bring to room temperature. Pat off excess marinade and season each side with freshly cracked salt and pepp
Heat CAST IRON SKILLET over high heat. Add 1 tablespoon vegetable oil. When it starts to smoke, reduce heat to medium-high and add steaks (working in 2 batches). Cook for 4 minutes without moving (SET TIMER). Add 2 tablespoons butter. Flip steaks with tongs (NOT a fork), and continue to cook for 4 more minutes. MEANWHILE…
Right after you flip the steaks, spoon melted butter over the steaks. Continue to baste steaks for the remaining cooking time, tilting the pan as needed to spoon the butter.
Check the internal temperature of the steaks after they have cooked a total of 8 minutes (they should be medium rare at this point). You want the temperature to register 5°F lower than the desired doneness (steaks will continue to cook after removing from skillet): For Medium Rare: 135°-140°, Medium: 140°-145°, Medium Well: 150°-160°.
If you wish to continue to cook your steaks, reduce heat to medium and continue to cook steaks to desired temperature, about 3-7 more minutes, flipping one more time and continuing to baste.
Transfer steaks to cutting board, and baste one more time and loosely tent with foil. Let rest at least 10 minutes before slicing against the grain. Serve with Mango Chimichurri.