Cook the pasta in boiling water until soft. Drain in colander.
In the pasta pot, melt the butter and stir in flour. Sauté for a couple minutes till browned and aromatic.
Whisk in milk and salt, pepper, garlic powder, and nutmeg. Heat and whisk till bubbly and starting to thicken. This will take some time but heat it low and slow. Heating it up too fast will break the sauce and make it grainy and it’ll never get thick.
Once the sauce is thick, add the cheese and stir till melted and smooth. Stir in the cooked pasta. Taste and season if needed and add more milk if desired.
Pour the cheesy pasta into a 9”x13” baking dish. Sprinkle the mixed cheddar and Parmesan cheeses on top.
Bake in 375 degree oven for 20 minutes until browned and bubbly. I like to broil it on high for about 3 minutes at the end to get a nice brown on top. Stand by the stove and watch it or you’ll burn it!
Serve while nice and warm and melty. Refrigerate leftovers.