Step 1In a medium saucepan, whisk together the stock, wine, ketchup, thyme and pepper. Bring to a boil over high heat, then lower the heat to medium and simmer until the mixture is reduced to 1 cup, about 30 minutes. Remove from the heat and set aside.
Step 1Coat the steaks on both sides with the olive oil and season evenly with the rosemary, salt and pepper. Let sit at room temperature for 20 to 30 minutes before grilling.
Step 2Prepare a charcoal fire covering one-half or two-thirds of the charcoal grate (a "two-zone" fire; if using a gas grill, turn flame to high heat). Sear the steaks over the fire, with the lid closed as much as possible, for 6 minutes, turning once and swapping their places as needed for even cooking. Then move the steaks away from the fire ("indirect heat"; if using a gas grill, reduce the heat to medium) and cook until done to your taste, 4 to 6 minutes for medium rare. Remove the steaks from the grill and let rest for 3 to 5 minutes.
Step 3Bring the sauce to a simmer and whisk in the butter until emulsified. Remove from heat. Carve the steaks and serve warm with the red wine sauce.