VARIATION
For Red Posole with Chicken, substitute 1 1/2 pounds boneless, skinless chicken thighs for the pork shoulder and reduce the cooking time to 20 minutes. After the pressure has released, using tongs, transfer the chicken to a cutting board, shred with two forks, and return the shredded chicken to the soup.
Note To make the posole as fat-free as possible, prepare it in advance, transfer to an airtight container, and refrigerate it for up to 2 days. Before reheating, use a spoon to remove the congealed layer of fat from the surface.