Macaroni with Cream and Cheese

Name: Macaroni with Cream and Cheese
Ingredients: 3/4 pound fresh poblano chiles (about 4); 1/2 large white onion, cut lengthwise into 1/4-inch-wide strips (1 3/4 cups); 1/2 teaspoon salt; 2 tablespoons unsalted butter; 1/2 fresh serrano chile, minced (1 teaspoon), including seeds; 2 large garlic cloves, minced; 1/2 teaspoon dried oregano (preferably Mexican), crumbled; 6 oounces dried cavatappi or penne; 2/3 cup crema or crème fraîche; 4 ounces queso fresco or mild feta, crumbled (1 cup)