Combine the chicken, vinegar, water, sugar, soy sauce, bay leaves, crushed peppercorns, onion, and garlic in a large pot; stir and bring the mixture to a boil for 2 minutes. Reduce heat to medium-low and cook at a simmer for 30 minutes.

Remove the chicken to a large serving platter and set aside. Increase the heat under the pot to medium and cook until the liquid reduces by about one-quarter, about 10 minutes. Season with salt; stir the coconut milk into the mixture. Cover and cook until the coconut milk appears oily, about 10 minutes. Pour the mixture over the chicken to serve.