To make artichoke crust, place the artichoke bottoms, thyme, garlic, buttermilk or yogurt, mustard, bread crumbs, salt and pepper in a food processor fitted with a steel blade and process until smooth. Sprinkle the salmon with the salt and pepper. Divide the artichoke crust into 4 portions and place dollops on the top side only of the salmon fillets. Pat down to form a crust. Cover the artichoke crust with the artichoke slices or sprinkle with bread crumbs. To make the mint vinaigrette, combine the tomato, shallots, mint, lemon juice, salt, pepper and vinegar in a small bowl. Set aside. Preheat oven to 350 degrees. Place a large non stick skillet over a medium high heat and when it is hot, add the salmon fillets skin side down. Cook until the skin is crispy, about 2 minutes. Transfer to the oven and bake until the salmon is rare, about 10 minutes. Serve immediately with the mint vinaigrette.