1. Take paper towels and blot the excess liquid off the pork shoulder. Then carve one-inch incisions all over the meat.
2. Process the garlic, cumin, oregano, pepper, and salt with half the oil in a blender. You want the mixture to result in a smooth paste. Set aside two tablespoons of the spice mix for later.
3. Rub the remaining garlic paste all over the pork, ensuring some of it is pushed into the incisions, then put the pork shoulder in the crockpot.
4. Program the slow cooker to LOW and cook for seven and a half to eight hours. By then, the meat should be fork-tender but not falling off the bone.
5. Pour the remaining olive oil into a pot and heat it till it shimmers. Then, saute the garlic paste for a minute until it’s fragrant. Then, turn off the stove, let the mixture cool, and whisk in the juices, Serrano pepper, and cilantro.
6. Drizzle this sauce over the pork and serve as desired.

Also, watch this video for more tips.