1 tablespoon achiote paste (can be substituted, see tip in directions)
1 fresh pineapple, peeled, cored and cut into rings ½ inch thick
¼ cup white vinegar
5 garlic cloves, peeled
1 tablespoon dried Mexican oregano
2 teaspoons ground cumin
¼ teaspoon ground cloves
½ teaspoon pepper
2 teaspoons salt
2 pounds pork shoulder, fat trimmed and thinly sliced ¼ inch thick
1 teaspoon sugar
4 guajillo peppers (optional), stems and seeds removed, then rehydrated in simmering water until softened
To build tacos:
1 pack corn tortillas
1 onion, small diced
1 bunch cilantro, roughly chopped
In a blender, add achiote paste, 3 pineapple rings, vinegar, garlic, oregano, cumin, clove, pepper, salt and guajillo peppers (optional). Blend until smooth; if necessary, add ¼ cup water to help blend smoothly.
In a large bowl, sprinkle sugar over pork and mix. Add marinade from blender and massage into pork, making sure that each piece of meat is coated.
Put 2 pairs of tongs facing each other at the bottom of the slow cooker (like two Pac-mans about to eat each other).
On a plate, stack pork and pineapple together. Layer 3 to 4 slices of pork and then a ring of pineapple. Repeat those layers until the stack reaches just below the height of the slow cooker.
Insert a spoon into the center of the stack to hold everything together. (If you are having trouble inserting the spoon, use a thin knife first to cut through the meat, then insert spoon.) Gently place your stacks in the slow cooker on top of the tongs.
Cook on high for 5 hours.
Allow to cool for 10 minutes. Carefully remove from slow cooker. With the spoons still in the center holding everything together, carve the meat and pineapples from the outside, working your way in (as you would a traditional al pastor or gyro).
Heat tortillas. Top each tortilla with al pastor and pineapple, and then finish with onions and cilantro.
Tip: If you are having trouble finding achiote paste, you can substitute 1 tablespoon paprika and 1 tablespoon chili powder.