Grape Chutney

Ingredients

• 1 medium red onion, finely chopped (3/4 cup)
• 1 tablespoon vegetable oil
• 1/4 cup Tawny Port
• 1/4 cup veal demiglace or stock
• 1/2 cup quartered seedless green grapes
• 1/2 cup quartered seedless red grapes
• 1/2 tablespoon finely grated peeled fresh ginger
• 1/2 tablespoon mustard seeds
• 1/2 tablespoon balsamic vinegar, or to taste
• 1 teaspoon kosher salt
• 1/2 teaspoon black pepper