Make the rub: Mix the coffee, chipotle, brown sugar, smoked paprika, salt and pepper. Press it firmly into both sides of the steaks and leave them out for 15 to 20 minutes to come to room temperature.
Blanch the potatoes: Boil the fingerlings in salted water for 3 minutes, then drain and leave to cool so they steam and turn slightly fluffy. Halve them lengthways once cool.
Sear the steak: Add the oil to a heavy pan over medium-high heat. When it just starts to smoke, lay in the steaks and sear for 3 to 4 minutes without moving them, then flip for 2 to 3 minutes.
Baste: Turn off the heat, then add the butter, thyme, rosemary and garlic. Tilt the pan and spoon the foaming butter over the steaks for 30 to 60 seconds. Rest on a board for 3 to 5 minutes.
Fry the potatoes: In the same pan, lay the fingerlings cut-side down so they catch the caramelised flavour. Spoon the steak's resting juices over them, crisp for a few minutes, then finish with a knob of butter.
Saute the mushrooms: Get a separate pan hot and dry, add the oil and mushrooms, and cook hard until the water steams off and they brown. Season, then add the shallot, garlic, thyme and a knob of butter.
Plate: Smear the barbecue sauce on the plate, sit the mushrooms then potatoes on top, slice the steak thick at an angle, and spoon over the last of the resting juices.
