One to two days before you cook your lechon, begin the marinating process. I typically let the pork shoulder marinade between 24-48 hours.
Using a medium size knife, make slits into the meat (not the skin side) and insert the garlic cloves deep into the meat. Then rub the sea salt all over the meat and skin of the pork shoulder. In a large oven-safe marinating bag, place the pork shoulder and the Cuban mojo.
Place the bag in a 9x13 baking pan and place it in the refrigerator for at least 24 hours. Once you're ready to roast, preheat your oven to 250 degrees. Remove the pork shoulder from the marinading bag and place it skin side up on a rack in a roasting pan
Pour the marinade that's inside the bag into the bottom of the roasting pan plus one cup of water. Using a knife, score pork skin to make strips across the skin. If you're feeling fancy, make a diamond pattern on the skin.
Loosely cover the pork shoulder with aluminum foil and place in the oven. Bake at 250 degrees for the first 2 hours then increase the heat to 350 degrees and bake until a meat thermometer reads 180°, 4–5 hours.
Remove foil; broil until the skin is crispy, 5–10 minutes. Be sure to watch the pork closely while broiling the skin as it can easily burn.
Remove from heat and allow to rest for 10 minutes before serving