Cook the penne pasta following the package instructions. Reserve ½ cup of pasta water before draining it.
Make the sauce:
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 half & half (or cream) and milk, stirring constantly. Add the grated cheese, salt, pepper, and nutmeg (if using) and combine. Reduce the heat and continue cooking the Alfredo sauce for about 5 minutes.
Combine:
Add the cooked pasta to the Alfredo sauce and toss to combine. If you like it more saucy, add some of the reserved pasta water (make sure it's hot) and stir.
Serve the penne with Alfredo, topped with additional parmesan cheese.
Storage & Reheating Leftovers
Once cooled, transfer to an airtight container and refrigerate for 3 to 4 days. Before reheating, add a couple of tablespoons of milk or half & half to reconstitute the sauce, then microwave it for a minute, stir, and then a little longer until heated through.