Add the clean chiles in a small saucepan and cover with water. Let it come to a boil. Turn off, and let the chiles hydrate about 15 minutes.
Place the garlic, cloves, pineapple, hydrated chiles and ¼ cup of the water where the chiles were hydrated in the blender glass.
Blend the lot. If necessary, add a bit more water. Taste it, and if you feel it too spicy, add a dash more vinegar.
Place the chicken pieces previously pat-dried in the bowl and season them over and under with salt.
Finely slice the onion and add it on top of the chicken.
Pour the thick sauce gently while mixing with the spoon or spatula.
Once everything is covered with the adobo sauce, cover with plastic wrap and leave it in the refrigerator for at least 8 hours.
Preheat your oven at 180 °C or 350 °F. Then, set your cast iron pan on the stovetop to heat as well with a drizzle of oil.
Drip the chicken pieces on a baking sheet with a rack on top.
Sear the pieces, one by one and on both sides starting on the side of the skin. Once well seared, set aside on the rack the pieces once more.
Once all the chicken pieces are seared, sweat the onion with a pinch of salt. It won't need much time. Maybe just a couple minutes.
Distribute the onion throughout the pan's surface and the chicken pieces in one even layer. If you need to use a second pan, use it.
Bake for about 20 minutes. Verify the chicken is cooked to 75 °C or 165 °F.
Personally, I like serving the pieces already deboned. So what I do is debone and either cut or mix the meat to mix with the now caramelized onions for my guests to prepare their tacos family style.
Notas/Notes
* This recipe is adapted from the Tacos al Pastor recipe from the book Mexico: The Cookbook, Margarita Carrillo Aponte, Phaidon.