Aromatic Braised Chicken with Fried Onions

Name: Aromatic Braised Chicken with Fried Onions
Ingredients: 2 1/2 pounds chicken thighs with bone, skin discarded; 4 medium shallots, quartered; 5 garlic cloves, chopped; 1 tablespoon minced peeled ginger; 2 sprigs fresh curry leaves, leaves removed from stems; 1 teaspoon cayenne; 1/4 teaspoon black peppercorns; 10 whole cloves; 1 (1-inch) piece cinnamon stick; 1 teaspoon distilled white vinegar; 1/2 cup water; About 2 cups vegetable oil; 1 medium onion, thinly sliced; 3 teaspoons all-purpose flour, divided