Preheat oven to 375 degrees. Cut each chicken breast in half lengthwise. Remove skin and bones. Pat breasts dry with paper towels. In a large baking dish, melt butter. Arrange breast halves side by side in dish, fleshy side down. Sprinkle with salt and pepper, turn breasts over, and sprinkle other side. Distribute onion and garlic evenly among and beneath breasts. In a small bowl stir together sour cream, Worcestershire sauce, salt, and pepper. Pour over chicken breasts to cover completely. Sprinkle with bread crumbs and paprika Bake chicken 30 minutes. Add half of the wine, pouring it in along edge of dish. Bake chicken another 20 minutes and add the remaining wine, again pouring it along edge of dish. Continue baking chicken until tender (15 to 30 minutes).