Roughly chop 1/2 an onion and peel 3 garlic cloves. Add the onion and garlic to a dollop of oil in a saucepan and saute on medium heat for 5-8 minutes.
Remove the stems and de-seed the dried chiles. Wipe off any dusty crevasses and tear the chiles into smaller pieces.
Add the chiles to the onion mixture along with 3 cups of water, 1/2 teaspoon Mexican oregano, 1/2 teaspoon cumin, 1/2 teaspoon salt, and freshly ground black pepper.
Bring mixture to a boil. Slice a chicken breast in half lengthwise and add it to the mixture. If the chicken isn't fully submerged add a bit more water. Reduce heat to a simmer and partially cover.
Cook for 10-15 minutes, or until the chicken is cooked through. Set chicken aside, covering in foil to retain moisture.
Add the remaining sauce mixture to a blender and combine well. (Always use caution when blending warm ingredients.)
And now take a taste of the sauce. If it tastes bitter to you then you're a candidate for some sauce sweetening.
Strain the sauce, pushing the mixture through a sieve using a spoon.
Return the strained sauce to the saucepan and simmer over medium heat. Add 1 Tablespoon of adobo sauce and a sliver of chocolate (both are optional).
Let simmer until reduced to a thicker consistency, approximately 15-30 minutes
Take a final taste for salt.
Shred the chicken using two forks and combine in a bowl along with a pinch of salt, some finely chopped onion, and a few spoonfuls of the sauce.
Warm up 8-10 corn tortillas in the oven for a couple minutes. (Or cover them with damp paper towels and nuke them for 60 seconds.)
Add a few spoonfuls of the sauce to a plate. Dredge a tortilla in the sauce and then flip it over, filling it with the chicken mixture and cheese.
Roll tight and add to a baking dish seam side down. You can line the baking dish with sauce to prevent sticking.
Continue rolling until all the chicken is gone. Add the remaining sauce to the top of the enchiladas.
Bake at 400F for 8-10 minutes. Serve immediately. Optional garnishes include Crema and Cotija cheese.