Ingredients

Partially freeze your pork butt for a couple of hours to make it easier to slice, then pound it out thinly. You can also ask your butcher toslice it for you.
Marinate the pork butt slices in the fridge for 4-8 hours.
To make the trompo, cut a thick slice of pineapple for the base and push a thick wooden skewer through it. Place on a baking sheet or cast-iron skillet. Slow roast in the oven for 2 1/2 to 3 hours at 275°F, or until the internal temp reaches 145°F. During the last 30 minutes or so, begin basting the pork with the pan juices.
*This is not required but visually looks better - during the last 10 minutes, rotate the trompo on it's side, baste in juices, and set under the broiler for 2-3 minutes, rotating until all sides have become caramelized and crispy.
Let it rest for 10 minutes before cutting into it.
Thinly slice the pork. The inside will not be caramelized &crispy like the outside - taqueros usually finish the al pastor on a griddle to achieve that. Using the pan juices, cook some sliced onions, pineapple, and al pastor seasoning on a pan for a few minutes. Once nice and caramelized and the onions have softened, its ready to serve.
Serve on corn tortillas and topped w/cooked onions, pineapple, onions, cilantro, and salsa verde.