I first tasted this dish (or one very nearly like it) on the end of a barely inhabited island located a few miles off the Côte d’Azur. But in France nowhere is so remote that you can’t find a good meal — in this case at a gracious, Michelin one-star restaurant in the hotel Mas de Langoustier. Chef Joel Guillet takes a contemporary approach to Provencal cooking , but one dish on his menu may date back to the Phoenicians. According to local lore, the red wine, olive, and caper sauce known as raïto originated in Greece and was brought to Massilia (as Marseilles was known in ancient times) by Phoenician sailors. Provence is the only place in France where you find it, and it’s rooted deeply enough to have several names, including rayte and raïte. Whatever its origins, it’s a sauce richly rooted in the Mediterranean, with a deep flavor that goes with grilled tuna.
Step 1: Prepare the fish: Brush the tuna steaks on both sides with the 2 tablespoons of olive oil and season them with salt and pepper to taste. Place the tuna in a baking dish, cover it, and let marinate, in the refrigerator, for 30 minutes.
Step 2: Make the raïto: Heat 3 tablespoons of olive oil in a large saucepan over medium-high heat. Add the onion and garlic and cook until golden brown, about 5 minutes. Add the tomato and cook for 2 minutes. Stir in the red wine, tomato paste, thyme, bay leaf, olives, and capers and bring to a boil. Reduce the heat to medium and let simmer briskly until the raïto is reduced by half, about 10 minutes.
Step 3: Remove the raïto from the heat and discard the thyme sprig and bay leaf. Whisk in the remaining 2 1/2 tablespoons of olive oil and season the raïto with salt and pepper to taste; the raïto should be highly seasoned. Cover the raïto and keep it warm.
Step 4: Set up the grill for direct grilling and preheat to high.
Step 5: When ready to cook, brush and oil the grill grate. Arrange the tuna steaks, facing in the same direction, on the hot grill grate. Grill the tuna steaks until cooked to taste, 1 to 2 minutes per side for rare, 2 to 3 minutes per side for medium-rare, turning them carefully with a long spatula. For an attractive crosshatch of grill marks, rotate the tuna steaks 45 degrees after the first minute of grilling on each side.
Step 6: Transfer the steaks to serving plates or a platter and serve at once, with the raïto spooned on top.
Chef Guillet likes the refinement of pureeing the raïto in a blender, adding the olives and capers at the end instead of before the sauce is reduced; he returns the raïto to the pan just to heat it through. Being a robust sort of guy, I like the gustiness of unpureed raïto. Take your choice.