Combine coffee, peppercorns, 1/4 cup brown sugar, salt, garlic, cayenne pepper and paprika in a small bowl. Press firmly onto steaks. Let steaks rest, covered, for 30 minutes at room temperature.
To cook, heat oil in a large saute pan until almost smoking. Add steaks and sear 2 to 3 minutes on each side. Do not overcrowd the pan. Use 2pans if needed. Remove steaks to a baking dish and finish cooking in the oven until desired doneness. Remove to a cutting board or platter and let rest 10 minutes before slicing.
Meanwhile, bring stout to a simmer in a small saucepan and reduce by about 1/3. Remove from the heat and whisk in the butter and 2 tablespoons brown sugar. After steaks have rested, pour any juices from the cutting board into the sauce, and serve with steaks.