Instructions

1. Preheat oven to 400°F. Cook pasta according to package directions, reducing cook time by 2 minutes. Drain.
2. Meanwhile, melt 1 Tbsp butter in a Dutch oven over medium-high heat. Add mushrooms and onion; cook 6 minutes or until onion is crisp-tender, stirring often. Stir in salt and pepper; transfer to a bowl.
3. Meanwhile, melt 2 Tbsp butter in Dutch oven over medium heat; whisk in flour, and cook, whisking constantly, 2 minutes. Whisk in 1 tsp thyme.
4. Gradually add milk to flour mixture, whisking until smooth. Bring to a simmer; cook, whisking constantly, until thickened. Remove from heat; stir in cheese.
5. Add cooked pasta to cheese sauce. Stir in mushroom mixture; spoon into a greased 9-inch square baking dish.
6. Melt 1 Tbsp butter in a small bowl; add breadcrumbs, tossing to coat. Sprinkle over mac and cheese. Bake 20 minutes or until golden brown and thoroughly heated. Sprinkle with ½ tsp thyme.