Combine creme fraiche, chopped basil, vinegar, lemon juice, 1/4 tsp. salt, and pepper to taste in small bowl. Heat broiler. Arrange halibut on broiler pan; sprinkle with remaining 1/4 tsp. salt and pepper to taste. Broil, turning once, 6 in. from heat until fish flakes easily with fork, 8-10 minutes. Divide tomato slices among 4 dinner plates. Place 1 halibut steak on each plate with tomatoes and spoon basil sauce over fish. Garnish with basil leaves. Serve at once. Tip: Creme fraiche is available in the dairy case of some supermarkets. You can make it by mixing 1 cup heavy cream (not ultra-pasteurized) with 1 Tb. active-culture buttermilk in small bowl and letting it stand at room temperature until thickened, 12-24 hours. Refrigerate covered at least 4 hours. Nutritional Value: Protein 51 g, fat 23 g, Carb 4 g, Sodium 555 mg, Total calories per serving: 427