3 cups (750 mL) elbow macaroni, about 450 g
3 tbsp (45 mL) butter
3 cloves garlic, minced
1 tsp (5 mL) fresh thyme, chopped
1/3 cup (75 mL) all-purpose flour
4 cups (1 L) milk
2 tbsp (30 mL) Dijon mustard
1/4 tsp (1 mL) grated nutmeg
1/4 tsp (1 mL) salt
1/4 tsp (1/4 tsp) pepper
Pinch cayenne pepper
1-1/2 cups (375 mL) Gruyère cheese, shredded
1-1/2 cups (375 mL) extra-old cheddar cheese, extra-old Cheddar cheese
1/2 cup (125 mL) panko bread crumbs
1/4 cup (60 mL) parmesan cheese, grated
1 tbsp (15 mL) butter, diced and softened
Meanwhile, in large saucepan, melt butter over medium heat; cook garlic and thyme, stirring occasionally, until fragrant, about 2 minutes. Whisk in flour; cook, whisking constantly, for 2 minutes. Pour in milk in slow steady stream, whiskingconstantly until smooth; cook, whisking often, until thickened, about 7 minutes. Whisk in mustard, nutmeg, salt, pepper and cayenne pepper. Stir in Gruyère and Cheddar cheeses until smooth; stir in pasta. Scrape into lightly greased 12-cup (3 L) casserole dish.
Topping: In bowl, combine panko with Parmesan cheese; using fingers, rub in butter until mixture resembles coarse sand. Sprinkle over pasta mixture.
Bake in 400 degrees F (200 degrees C) oven until sauce is bubbly and topping is golden, about 25 minutes. Let stand for 10 minutes before serving.
Tip from the Test Kitchen: The sauce might seem a little runny at first, but it will thicken beautifully when baked with the starchy macaroni.