Take your Rib Eye Steak (2) out of the fridge about 1 hour before you're ready to cook to bring the steaks to room temperature. Put your cast iron skillet in the oven, then preheat to 500 degrees F (260 degrees C). Make sure your kitchen is well ventilated.
In a small bowl, mix Ground Coffee (3 tablespoon), Dark Cocoa Powder (1 tablespoon), Brown Sugar (2 tablespoon), Garlic Powder (1 teaspoon), Salt (1 teaspoon), Ground Black Pepper (1 teaspoon), Smoked Paprika (1 teaspoon), and Dry Mustard (1 teaspoon).
Smear Unsalted Butter (2 tablespoon) all over the steaks, then rub in generous amounts of coffee dry rub on each side of the steaks.
Turn on your stove's burner. Using over safe gloves, take your skillet out of the oven and place it on the burner. Place the steaks on the skillet for 30 seconds on each side.
Place skillet back in the oven and let the steaks cook 2 minutes per side to achieve medium rare. For well done, add 1 minute to each side.
Remove the steaks from the skillet and let them sit on a plate for 5 minutes before cutting into the steaks.