Roasted Onions

Bahan-bahan (4 porsi)

• 2 large sweet onions (1 ½ -2 pounds)
• 2 tablespoons melted butter
• 1 teaspoon balsamic vinegar
• 3 tablespoons water (or broth)
• ⅛ teaspoon kosher salt (or to taste)
• ⅛ teaspoon black pepper