In a blender or food processor, pulse the jalapeños until finely minced. Add the cilantro and pulse until chopped. Add the sour cream, buttermilk, ½ cup salsa verde, garlic powder, onion powder, salt, and pepper, and blend/process until the mixture is smooth and completely puréed. Adjust the seasonings to taste, adding more salt and pepper if necessary. Cover and refrigerate for at least 4 hours (ideally 8+ hours), to allow the flavors to blend and the sauce to thicken.

Remove the creamy jalapeño sauce from the refrigerator to come to room temperature. Heat a large saucepan over medium heat; add the olive oil and swirl to coat. Add the chicken to the pan and allow it to cook for a few minutes until just heated through, stirring frequently to prevent sticking. Stir in the garlic and cook for another 30 seconds or until fragrant. Remove the pan from the heat and stir in the remaining salsa verde plus ½ cup of the prepared creamy jalapeño sauce; set aside.

Preheat the oven to 350°F. Spread a thin layer of creamy jalapeño sauce in the bottom of a large, deep baking dish.

Place the tortillas on a plate, cover with a damp paper towel, and microwave for 30 seconds to 1 minute or until warm and pliable; cover and keep warm. Spread a generous spoonful of chicken mixture down the center of each tortilla. Add a pinch of shredded cheese on top. Roll the tortilla around the filling and place it seam side down in the baking dish (the enchilada should be full but not overstuffed). Top the enchilada with a spoonful of sauce and spread all over to keep the tortilla moist and reduce the odds of splitting while you prepare the rest of the enchiladas.

When all of the enchiladas are in the dish(es), evenly pour the rest of the creamy jalapeño sauce over the enchiladas, covering them completely. Sprinkle the remaining shredded cheese on top of the sauce. Bake for 30 minutes or until golden and bubbly. Garnish with cilantro and/or sliced pickled jalapeños, if desired.