Season the chicken with salt and pepper, and grill or bake at 350 for 30 minutes, or until no longer pink; cool then shred.
Rinse and husk the tomatillos and the jalapenos; roast them on a baking sheet for about 5 minutes per side. Cool, then transfer with any juices to a blender and puree.
Heat the oil in a medium saucepan over medium high heat. When its hot, add the puree and stir occasionally for about 5 minutes.
Add the chicken broth and simmer over medium heat for about 10 minutes.
Taste and season with salt, usually about 2 teaspoons.