Bring a large pot of water to a boil with a pinch of salt. Once the boil starts add the tomatillo, onion, garlic cloves, cilantro and the serrano chiles (you can put more than required if desired depending the spice you like). Boil in max heat for 15 minutes or until the ingredients are soft and they are less brighter.
Drain the water, put the ingredients on the blender and make a light puree (Salsa Verde).
In another pot, boil water, and add the chicken. Cook until it´s tender take out and reserve. Let the chicken breast cool until easy to handle, shred and reserve.
Return the salsa verde to the pot and add the shredded chicken, bring them to a boil and reserve.
In a large, 15x10 rectangular glass baking dish first put a spoon of salsa verde to cover the bottom, then add a layer of pasta until it covers the salsa, add a thin layer of chicken en salsa verde, 3oz Manchego cheese and cover again with a layer of pasta, repeat the procedure and finish with sour cream and a layer of cheese
Once finished, cover with aluminum foil and put into the oven at 375º for 20 minutes. Once these 20 minutes are over take off the aluminum foil and put back 10 more minutes at the same temperature or until the cheese gets a Brown color.
