Instant Pot Mac and Cheese

  (16 oz) box medium pasta shells (uncooked)

  cups vegetable broth

  teaspoon salt (more or less to taste)

  teaspoon black pepper (more or less to taste)

milk (plus more, if necessary)

shredded parmesan (about 2 oz)

shredded gruyere (I used a hickory smoked)

block sharp cheddar cheese (shredded)