Mexican Street Tacos (Tacos Al Pastor)

‍Marinade:

1. Place the ancho and guajillo chiles in a heatproof bowl, and carefully pour in boiling water until they’re submerged. Allow chilies to reconstitute until they’re pliable and easy to tear, about 10-15 minutes. 
2. In a blender combine the white vinegar, pineapple juice, achiote paste, garlic, brown sugar, cumin, cinnamon, and salt. Add the drained chilies, cover and blend on high speed until thick and smooth.
3. Working from the short end, slice the pork shoulder into ½ inch-thick slices. Transfer to a large mixing bowl and add the marinade. Toss well to evenly coat the meat. Cover with plastic wrap and let it marinate overnight in the fridge

‍Grilling:

1. On a large wood cutting board, stand 3-4 metal skewers with one hand, with the pointed tips facing up. Spread the skewers slightly to avoid creating a tight cluster. With the flat side facing down, carefully pierce one marinated pork slice and slide it down to the looped end of the skewers. Repeat with the remaining pork until all the meat has been tightly stacked together onto the skewers.
2. Using a large outdoor grill, preheat only two-thirds of the grill to medium-high heat. Using long tongs, rub the hot grates with a folded up paper towel coated with vegetable oil. Sear the al pastor stack on the hot grates 2-3 minutes per side until some color forms.
3. Stand the base of the skewered meat onto the grill and cook until slightly charred, about 2-3 minutes. Turn the skewered meat onto its side and continue to cook until all sides have been seared and slightly charred.
4. Place the meat onto the cold side of the grill, cover and grill-roast between 350°F-400°F for 1 ½ to 2 hours, rotating occasionally.
5. Remove meat, wrap in foil and let it rest for 20 minutes. 

‍Pineapple Relish:

1. Cut off the top and bottom of the pineapple. Stand the pineapple upright and shave off the outer skin by slicing down the sides. Cut the pineapple into quarters, lengthwise. 
2. Preheat the grill to high and using long tongs, grease the grates with a folded up paper towel coated in vegetable oil. Arrange the pineapple quarters, jalapenos and onions onto the hot grill and cook until all sides are nicely charred, 10-12 minutes for the pineapples and 5-8 minutes for the jalapenos and onion.  
3. Chop the grilled pineapple and onions into bite-sized pieces and transfer to a medium mixing bowl. Slice the grilled jalapenos thin and add to the bowl. Add the cilantro, lime zest and juice. Season generously with salt and mix well until combined.

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Assembly:

1. Stand the skewered meat on a large cutting board. Slice the meat by running a large, sharp knife down the sides, turning it slightly after each slice. The meat slices can be thick or thin. 
2. In a cast iron skillet or a griddle set over medium-high heat, lightly char corn tortillas, about 30 seconds per side.
3. To build a taco, place some al pastor meat down the center. Top with grilled pineapple relish, and finish with a squeeze of lime juice. If using, arrange a slice of avocado and sprinkle with grated Cotija cheese.