Cook the pasta following the instructions on the box. When the pasta is ready, drain the water and leave the pasta in the colander.
Make the sauce:
In the same pot from the pasta over medium heat, melt the butter. Add the garlic and stir to toast it for about a minute, ensuring it doesn’t burn.
Pour in the cream (or half and half) and milk and stir constantly. Add the grated cheese, salt, pepper, and nutmeg (if using) and combine. Reduce the heat, continue cooking the Alfredo sauce for about 5 minutes, and turn off the heat.
Combine:
Add the pasta to the Alfredo sauce in the pot and stir. Serve as is, or continue with the cheesy crust step below.
Cheesy crust:
Transfer the macaroni and cheese into an oven-safe baking dish and sprinkle the grated cheddar on top of the pasta.
Place the baking dish in the oven, with the top rack positioned a little higher than halfway up but not too close to the top of the oven. BROIL the cheesy dish for 3 minutes, until the cheese is melted and lightly browned but not burned. Remove it from the oven and serve.
Notes
You can swap the garlic clove for ½ teaspoon of garlic powder.