Green Tomatillo Enchilladas

This is my first great find, Tomatillo Enchilladas from Williams-Sonoma Website. I am bored with the old Las Palmas Enchillada Sauce packed with sodium, oil and crap. My search began with finding a good basic enchillada sauce recipe. Still looking for a great red sauce.

Salud! Thanks W-S!

2 lb. chicken breasts (I cooked a whole chicken in the crock pot with S&P)
1/4 white onion
1 garlic head, halved crosswise
1 Tbs. sea salt
For the sauce:
3 lb. tomatillos, husked and rinsed
9 serrano chilies (I used 4)
3 garlic cloves, chopped
1/4 cup safflower or canola oil
1 Tbs. sea salt, or to taste
For the enchiladas:
1/3 cup safflower or canola oil
18 thin corn tortillas (mine made 20)
1 cup crema or crème fraîche (I used sour cream)
1 white onion, thinly sliced (I marinated these in apple cider vinegar thanks to Rick Bayless's tip)
1 cup crumbled queso fresco
Directions:
To prepare the chicken, place in a saucepan with the onion, garlic and salt and add water to cover. Bring to a boil over high heat, reduce the heat to medium, cover and simmer until the chicken is cooked through, 20 to 25 minutes. Let cool and lift out the chicken, saving the broth for another use. (The chicken can be wrapped and refrigerated for up to 1 day before continuing.) Discard the skin and bones and shred the meat with your fingers. You should have 4 cups chicken. To make the sauce, in a saucepan, combine the tomatillos and chilies with water to cover. Bring to a boil over medium-high heat and cook until tender, 10 to 15 minutes. If some of the tomatillos remain firm, the pan should still be removed from the heat. Drain and, working in batches, place the tomatillos and chilies in a blender along with the garlic. Process until a smooth sauce forms. In a fry pan over medium-high heat, warm the oil until it is smoking. Quickly add the tomatillo sauce and fry, stirring constantly, until the sauce begins to bubble. Reduce the heat to low and cook until the sauce starts to thicken, 5 minutes more. Add the 1 Tbs. salt; taste and add more salt, if needed. Keep warm. When the sauce is combined with the tortillas and chicken, the taste of salt will be quite diminished; it should be highly seasoned at this point. You should have 3 cups of sauce. If needed, add some of the chicken broth. Preheat an oven to 350°F. To make the enchiladas, in a fry pan, heat the oil over medium-high heat until sizzling hot. Using tongs, quickly pass each tortilla through the oil to soften, then drain on paper towels. Using your fingers, dip each tortilla briefly in the warm sauce, place on a plate, put a large spoonful of shredded chicken near one edge and roll up the tortilla. Place, seam side down, in a baking dish. Cover with the remaining sauce. Bake until thoroughly heated, about 10 minutes. Remove the enchiladas from the oven and top with the crema, onion slices and crumbled cheese. Alternately, arrange the enchiladas on individual warmed plates and garnish before serving. Serve immediatelyenchiladas become soggy quickly.
Serves 6.