Preheat your oven to 325 degrees with the rack in the middle.
Cut your pork shoulder into 1 inch chunks and season with your spice rub (cumin, paprika chili powder, salt, oregano, and pepper).
In a Dutch oven over medium high heat, add a bit of olive oil and sear your meat on all sides. Once all of the meat has a good sear on it, add your chicken stock, lime juice, garlic, onion, and bay leaves.
Place it in the oven with the lid on, and cook for 4 hours. To test meat if the meat is done, use a fork to see if it easily shreds. You could also use a thermometer to check the internal temperature; pork should be cooked to 145 degrees Fahrenheit.
When your meat is done cooking, remove all of the meat from the cooking liquid and place on a large cutting board. Remove the onions and garlic from the cooking liquid with a slotted spoon and discard.
Using two forks, shred the meat into bite-sized pieces. Add all of the shredded meat back into the pot with all the flavorful liquid and stir until everything has been coated well.
Transfer the soaked meat (letting excess liquid drip off the meat) onto a baking sheet lined with tin foil. Turn the oven on to a low broil and place the sheet of carnitas directly under the flames. Let your meat broil for 5-10 minutes (may be more may be less depending on your broiler). The carnitas will be done when you see the tops starting to crisp.
Plate up the carnitas, Squeeze fresh lime over the carnitas to taste. Serve and enjoy!