Double-Cheese Macaroni and Greens

Cook the pasta according to package directions, adding the chard during last 3 minutes of cooking. Drain the pasta and chard and return to the pot. Meanwhile, heat the oil in a large skillet over medium heat. Add the onion, season with 1/2 teaspoon each salt and pepper and cook, covered, stirring occasionally, until tender, 6 to 8 minutes. Sprinkle the flour over the onions and cook, stirring, for 2 minutes; whisk in the milk. Cook, stirring occasionally, until slightly thickened, 3 to 4 minutes. Add the Cheddar and 1/2 cup of Muenster cheese and cook, stirring, until melted. Add the pasta and chard and toss to combine. Heat broiler. Transfer the mixture to a 1 1/2-quart broiler-proof baking dish. Sprinkle with the remaining 1/2 cup Muenster and broil until golden brown, 3 to 4 minutes.