Melt the butter in a large pot over medium heat then add in the flour and stir to combine. Cook for 1 minute.
Pour in the water, and cook on medium heat until the mixture thickens slightly. This will take about 2 minutes.
Add in the milk and heavy cream, stir to combine then add in the macaroni pasta, salt, pepper, nutmeg, and ground mustard. Give it a quick stir and bring the mixture to a boil, then reduce to simmer.
Cook the pasta in the milk mixture for 9-10 minutes, making sure to stir often to keep the pasta from sticking to the bottom of the pan.
Remove the pot from the heat and add in the shredded cheese, stir until the sauce is smooth and creamy then serve immediately!