Bring steaks to room temp. Take them out of the fridge 20–30 minutes before cooking.
This helps them cook evenly.
Preheat the air fryer. Set it to 400°F (200°C) for 5 minutes. A hot basket helps form a great crust.
Mix the coffee rub. In a small bowl, combine ground coffee, brown sugar, smoked paprika, kosher salt, black pepper, garlic powder, onion powder, and cayenne (if using).
Pat steaks dry. Use paper towels to remove surface moisture. Dry steaks sear better.
Oil lightly. Rub a thin layer of oil on all sides of the steaks.
This helps the spice mix stick and promotes browning.
Apply the rub generously. Coat both sides and the edges with the coffee rub, pressing it in so it adheres. You should use most or all of the mixture.
Air fry. Place steaks in a single layer in the preheated basket. Cook 8–10 minutes for medium-rare, flipping halfway.
Aim for an internal temperature of 130°F (54°C) for medium-rare, 135–140°F (57–60°C) for medium.
Rest the meat. Transfer steaks to a plate and rest 5–7 minutes. This keeps them juicy.
Finish with butter and salt. Top with a small pat of butter and a pinch of flaky salt just before slicing, if desired.
Slice and serve. Slice against the grain and serve with a simple side like roasted potatoes, air fryer asparagus, or a crisp salad.