Place chicken in a large saucepan. Add 6 cups water, 1 teaspoon salt, 2 garlic clove, peppercorns and then bring to a boil. Reduce heat to low, cover and simmer 15 - 20 minutes. Remove chicken, pull meat from bones,shred and set aside.
Place tomatillos and chiles in a saucepan; cover with water and boil over medium-high heat for 8 minutes. Drain, reserving 1/2 cup liquid.
Transfer mixture to a blender and add remaining 2 cloves garlic, Cholula Green Pepper and cilantro. Blend until smooth, adding liquid if necessary.
Heat oil in a small saucepan over medium-high heat. Add tomatillo-chile puree and reduce heat to medium. Simmer, stirring constantly for 10 minutes. Reduce heat, add sour cream and remaining 1 teaspoon salt. Stir about 1 minute then set aside.
Preheat oven to 350°F. Warm tortillas 10 seconds per side in a skillet over medium heat. Divide shredded chicken evenly among tortillas and roll up. Spread 1/3 sauce in a 9" baking dish. Arrange enchiladas in 1 layer, seam side down. Cover with remaining sauce and sprinkle with cheese.
Bake 30 minutes or until cheese starts to brown.