Step 1 Rub 1 teaspoon of the salt into the duck breasts, place them in a large sealable plastic bag and refrigerate for 1 hour while you make the sauce.
Step 2 Soak the chiles de arbol and dried cherries in 2 cups of boiling water for about 30 minutes. Drain, reserving the liquid. In a food processor, combine the drained chiles and cherries with one-fourth cup olive oil, one-half teaspoon salt and 2 cloves of the minced garlic. Process to a thick paste, adding a little of the reserved liquid to help combine and adjust consistency. Set aside. This makes about 1 cup compote.
Step 3In a medium, heavy-bottomed saucepan over medium heat, place the remaining 2 tablespoons of olive oil, the onions and the remaining 3 cloves of minced garlic. Saute until the onions are just starting to caramelize, about 5 minutes. Add the tomatillos and remaining one-half teaspoon salt. Cover and continue to cook about 8 to 10 minutes, stirring occasionally, until the tomatillos are tender. Remove and cool slightly for a few minutes.
Step 4In a food processor, combine the tomatillo mixture with one-fourth cup of the chile-cherry paste. Set aside. This makes about 1 1/2 cups sauce.
Step 5Place the duck breasts, skin side down, into a cold, cast-iron skillet. Turn the heat to medium-high and cook the duck about 10 minutes, or until the skin is golden-brown and crispy and the fat has rendered off. (Turn the heat down to medium after a few minutes and watch to make sure the duck doesn't burn. Adjust the heat if necessary so that it cooks evenly.) Turn the duck over and cook for 1 minute to cook the meat to medium-rare; otherwise, continue cooking until desired doneness is achieved. Remove the breasts to a cutting board and let rest for 5 minutes. Slice very thinly on the diagonal.
Step 6Heat a skillet over medium heat and warm the tortillas. Place two to a plate and divide the sliced duck among the tortillas. Spoon a tablespoon or so of the tomatillo sauce over the duck and add a half-teaspoon of chile-cherry compote on top, or to taste. Sprinkle the top with fresh chopped cilantro. Serve immediately.