This masterpiece is everything you could ever want in the classic dish—elbow noodles, two kinds of melty cheese, and bits of ham.
1. Preheat oven to 350°F. Cook the macaroni for half the time of package directions.
2. Meanwhile, into a large bowl, coarsely grate the Cheddar and Monterey Jack cheeses, reserving 1 cup for topping. Stir in drained macaroni and ham. Transfer to 2½-qt baking dish.
3. In a medium bowl, whisk the flour, mustard powder, onion powder, and eggs together. Whisk in the sour cream, milk, and ¾ tsp salt. Season with black pepper. Pour over macaroni in baking dish. Stir to combine. Top with reserved grated cheeses.
4. Bake 30 min., until bubbly and custard is set. Let stand 10 min. before serving.
For a golden brown top, use a broiler-safe baking dish and broil for 2‒3 min. after baking. Garnish with chopped chives.