1. Heat oil in a large skillet over medium heat. Add pancetta, and cook 5 minutes or until it begins to crisp. Add Brussels sprouts, onion, and garlic, and sauté until golden brown.
2. Add 3 cups water, chestnuts, and next 3 ingredients. Reduce heat to low, and cook 1 hour. Add butter, and stir until melted. Season with salt and pepper.