Chicken & Sauce:
This recipe can be made with fresh or frozen bone-in chicken breast with or without skin or fresh or frozen boneless chicken breast. If using frozen, the key factor is that it will need to be able to be separated if all frozen together, so it will fit in the pot. If using skin on, the skin will be discarded, either before or after cooking, your choice. The timing and method will vary slightly depending on the type of chicken used.
For Serving:
Strain Rotel and place the juices in a measuring cup. There should be about 1/3 of a cup. Add enough water to bring it up to the one-cup mark on the measuring cup. Add to the Instant Pot. Place the chicken in the pot: If bone-in add directly on top of the liquid. If boneless, place it on the wire rack that came with the Instant Pot.
Sprinkle the chicken with the oil if using skinless breasts (it helps the herbs stick and helps keep the chicken moist.) Sprinkle with salt, marjoram, and pepper. Add the small pinch of cloves. Place the garlic, reserved Rotel tomatoes, and chipotle peppers on top of the chicken. Sprinkle vinegar over the tomatoes. Tuck the onions where they’ll fit.
Seal the Instant Pot and using the Poultry setting or Pressure setting on high, set as directed.
When finished, allow to naturally release for 10 minutes before releasing any remaining pressure. Check chicken for doneness. Cooking time might vary depending on the size of the individual breasts and the shape of the chicken. If it needs more time, replace the lid, seal, and bring back to pressure for another minute or two.
Remove chicken from pot, allowing the tomato mixture, herbs, etc., to fall (they may need to be nudged off) back into the liquid. Set chicken aside to rest until cool enough to handle.
In the meantime, strain the juices from the solids in the pot. (Set pot aside, no need to wash.) Place the solids into the blender with about two cups of the juices. (Save the remainder of the juices in case the final dish needs to be moistened.) Process the blender until the mixture is broken down; it doesn’t need to be completely smooth.
Add the blender mixture back to the instant pot, turn on the saute function, and cook, stirring often, until the mixture is about the consistency of spaghetti sauce; when a spoon is run through, the trail left behind should not fill in immediately.
While the sauce simmers, if using chicken with bones or skin, remove the meat. If not, proceed: Shred the chicken by hand or with a mixer, into small shreds combined with smallish bite-sized pieces. Add to the Instant Pot, gently mix in with the sauce, and allow to simmer for a minute or two to heat through. The chicken should be moist but not wet. If too dry, moisten with the reserved liquid, or if too wet, simmer for a minute or two longer to thicken. Taste for seasoning and add more salt or vinegar if desired.
Serve as tostadas garnished as suggested, or serve as suggested in the body of the post.
Note: You’ll likely end up with some juices left over. These make a great base, along with a little chicken broth for all kinds of Mexican or Southwestern-leaning soups.