Lay the pork loin fat-side down. Cut it through to the fat in about 1-2? wide strips. Be careful not to cut all the way through the fat! The “strips” must still be attached by the fat.
Mix the cumin, oregano, red pepper flakes, chili-lime powder, chicken bouillon, black pepper, salt in a small bowl. Coat the pork loin with spice mixture, including the fat side and down into all the cuts.
Put the pork loin fat-side down in a large heavy-bottomed pot set over medium heat. Pour the vegetable oil into the pot around the pork loin. Cut the ends off the onion, peel off its skin, cut the onion in half. Then cut it into wedges. Arrange the onion wedges in the pot around the pork loin. Add the habanero peppers, garlic, and bay leaf to the pot.
Pour the orange juice into the pot surrounding the pork loin, being careful not to wash the spices off it. Add the lime juice and milk, again trying not to wash the spices off the pork loin. Cut the butter into smaller slices and add to the broth.
Add enough water to just cover the pork loin, about 1/2 to 1 cup.
Reduce heat to low and simmer covered for about 3 hours. Remove the pork loin from the pot. It should be falling apart at this point. Preheat oven to 400 degrees Fahrenheit. Using a large fork, press the meat apart into smaller bite-size pieces. This will be very easy to do as the meat should be very tender and easily fall apart.
Put the pulled pork (carnitas) into an oven dish and add the onions. Spoon some of the broth from the pot over the meat. Toss the meat to cover it thoroughly with the broth. Discard the remaining broth in the pot, or freeze it to serve as a base for another dish.
Bake the carnitas for about 15 minutes until the broth cooks off and the tips of the meat are a bit crispy. If there´s still broth in the dish, remove it from the oven, toss the meat in the juice again, put it back in the oven for another 5-10 minutes or so, and then remove.
Enjoy the carnitas with warmed corn tortillas, beans, and pico de gallo.