¾ pound elbow macaroni, cooked according to package directions
Garnish: fresh thyme, ground black pepper
Instructions
Heat a 12-inch cast-iron skillet over medium-high heat. Reduce heat to medium; add 1 tablespoon butter, stirring until butter is melted. Add onion, ¼ teaspoon salt, and ¼ teaspoon pepper; cook, stirring frequently, until onion is golden brown and softened, about 8 minutes. (Onion will not be tender at this point.) Stir in 2 tablespoons water. Reduce heat to medium-low; cover and cook, stirring occasionally, until onion is very soft, about 45 minutes. Remove from skillet.
Preheat oven to 350°.
In a large saucepan, melt remaining 4 tablespoons butter over medium heat. Whisk in flour; cook for 1 minute, stirring constantly. Whisk in milk, thyme, remaining 1¼ teaspoons salt, and remaining ½ teaspoon pepper. Bring mixture to a simmer, whisking constantly. Remove from heat. Add ¾ cup cheese, stirring until cheese is melted.
In a large bowl, stir together cooked pasta, onion, cheese sauce, and ¾ cup cheese. Spoon pasta mixture into skillet. Cover with foil.
Bake until heated through, about 30 minutes. Uncover and sprinkle with remaining ½ cup cheese. Bake until cheese is melted, 3 to 5 minutes more. Garnish with thyme and pepper, if desired.
Recipe by Taste of the South at https://www.tasteofthesouthmagazine.com/caramelized-onion-mac-cheese/