Preheat oven to 425°F and line a baking sheet with a large piece of foil; fold in the sides slightly to form a rim. Place grapes on foil and top with vinegar, olive oil, and sea salt. Stir lightly to coat grapes with mixture. Roast for 30 minutes, stirring every 10 minutes. Let cool slightly. Place cheese in a decorative shallow bowl and top with grapes. Sprinkle with pistachios and basil. Serve with baguette slices. Makes 8 appetizer servings.