1 small onion, sliced
3 cloves garlic, crushed
2 1/2 cups sauvignon blanc or other dry white wine
4 boneless, skinless chicken breasts
3 cups chicken broth
Salt and pepper
2 cups peeled, seeded and chopped fresh tomatoes
1/4 cup butter ( 1/2 stick)
2 tablespoons virgin olive oil
1/3 cup thinly sliced basil leaves

Combine onion, garlic and wine and bring to simmer. Carefully ignite fumes of wine (if flame blows out, reduce stove-top heat). When flame subsides, pour into noncorrosive container large enough to contain breast pieces without overlapping. Chill. Add breasts to cold marinade; they should be completely covered. Cover and refrigerate 24 to 36 hours.
Remove chicken breasts from marinade and set them aside. Strain liquid into small saucepan. Bring gently to simmer; do not allow mixture to boil. Skim surface of anything that floats to top. Continue simmering and skimming until wine is clear; this will take at least 20 minutes. Add chicken broth to wine and, skimming as it cooks, reduce gently to 1/2 cup. This will take about 45 minutes.
Remove chicken breasts from liquid and season them with salt and pepper to taste at least 5 minutes before cooking, then grill over medium-high heat until cooked through but still moist inside, 5 to 6 minutes a side. Add tomatoes to reduced wine and broth, bring to simmer and stir in butter by the tablespoon until incorporated. Add oil. Add basil leaves. Season to taste with salt and pepper. Divide sauce among 4 plates and top with grilled chicken breast.