Cook the pasta:
Bring a large pot of salted water to a boil. Cook the elbow macaroni according to the package instructions until al dente, then drain and set aside. Be careful not to overcook the pasta.

Make the roux:
In the same large pot, melt the butter over medium heat. Once the butter is melted, whisk in the flour and cook for 1-2 minutes, forming a roux to thicken the soup.

Add the liquids:
Gradually whisk in the chicken broth, milk, and heavy cream. Stir continuously to ensure no lumps form. Continue stirring until the mixture starts to thicken, about 5-7 minutes.

Add the cheese:
Once the soup base has thickened, stir in the shredded cheddar cheese gradually, allowing it to melt completely into the soup. Keep stirring until the soup is creamy and smooth.

Season the soup:
Add salt, pepper, and mustard powder (if using). Taste and adjust the seasoning. You can also add a splash of vinegar for more tang if desired.

Combine the pasta and soup:
Add the cooked macaroni to the soup and stir to combine. Let the soup simmer for an additional 5-10 minutes to allow the flavors to meld together and for the pasta to absorb some of the soup’s creamy goodness.

Serve and enjoy:
Once the soup is thick, creamy, and heated through, ladle it into bowls. Garnish with extra shredded cheese, fresh herbs, or a sprinkle of cracked black pepper if desired.