Heat a stovetop pressure cooker over medium high heat (or set your electric pressure cooker to "sauté"). Add the oil and brown the meat on all sides, until golden all around.
Add all remaining ingredients to the cooker. Close the lid and cook on high pressure for 90 minutes in a stovetop cooker (or 105 minutes in an electric cooker).
Depressurize, then remove the meat. Allow it to cool for a few minutes, then shred it with two forks.
Either mix it with as much of the cooking liquid as you like, we usually do all, as the meat will soak up the liquid and become incredibly juicy and flavorful. OR if you want to have crispy carnitas, add the meat to a skillet over medium high heat in batches, drizzling with the juice as you brown the bottom.
To freeze, cool the meat completely. Portion it out in freezer bags or mason jars, making sure to add cooking liquid, too. Freeze for up to 3 months. To reheat, simply thaw in the fridge overnight, transfer to a pot and heat until it is boiling, making sure the meat is evenly heated.