Bring a large pot of salted water to a boil.
Add macaroni and cook according to package instructions until just al dente.
Drain and set aside.
Melt butter in the same pot over medium heat.
Sprinkle in flour and 1 teaspoon salt, stirring to create a roux—cook until it looks like wet sand.
Slowly whisk in the milk and heavy cream—start with a bit, whisk well to avoid lumps, then add the rest.
Add garlic powder, ground mustard, and Worcestershire sauce.
Whisk gently; let sauce thicken until just starting to bubble.
Reserve about 1 to 1.5 cups of cheddar for the topping.
Stir in remaining cheddar and all Gruyère until sauce is smooth and melty.
Remove from heat.
Pour drained noodles into the cheese sauce and mix well.
Spray a 9×13 baking dish, pour everything in.
Sprinkle reserved cheddar evenly across the top.
Bake at 350°F for 10 minutes.
Switch oven to broil and cook for 2 minutes—no more! (This gives that golden-brown cheesy crust. Watch closely!)
Let the bubbly mac rest for a few minutes.
Scoop up both creamy centers and crisped edges onto every plate—don’t forget a little kindness for yourself or the lucky folks you’re serving!
Season every layer for deep flavor: salt the pasta water, season the roux, taste as you go.
Always grate your own cheese for meltiness—bagged cheese works, but fresh melts best.
Combining stove-top creaminess with a short bake and quick broil gives you the best of both worlds: