Chicken Enchiladas Verdes

Name: Chicken Enchiladas Verdes
Ingredients: 2 tablespoons olive oil; ½ onion, halved; 1 poblano chile, halved; 2 pounds tomatillos (about 20 medium), husks removed, rinsed; 2 serrano chiles, chopped; 3 garlic cloves, smashed; 1 cup homemade chicken stock or low-sodium chicken broth; ½ cup cilantro leaves with tender stems, chopped; 1 tablespoon fresh lime juice; Kosher salt; ½ rotisserie chicken, skin removed, meat shredded; ½ teaspoon ground coriander; ¼ teaspoon ground chile de árbol or red pepper flakes; 1 cup vegetable oil; 8 6-inch corn tortillas; 10 ounces Cotija cheese, finely grated, plus more for serving; ½ cup crème fraîche; 1 tablespoon milk; ½ red onion, thinly sliced