Preheat the oven 250 degrees F. Cut the tomatoes in half lengthwise. Gently squeeze out the seeds, discarding them. Place the tomatoes cut side up on a non-stick or parchment paper-lined baking sheet. Top the tomatoes with a few garlic slices. Drizzle with 2 Tbsp. of the olive oil and sprinkle with salt and pepper. Roast 1 hour. Remove and place in a food processor or blender with the stock and basil and process until smooth. Place mixture in a pot, adjust season if needed, and gently simmer over low heat. Heat the grill to medium-high heat. Brush the steaks with remaining oil and season with salt and pepper. Grill them 3-4 minutes per side; a little longer if you like them more done than medium rare. Divide and spoon the sauce on four plates. Top sauce with a steak and serve.