For the mac and cheese: Bring a large pot of salted water to a boil. Cook the macaroni until al dente (the lower range of the cooking time on the box). Reserve 1/2 cup of the cooking water before draining, then return the macaroni to the pot. Add the butter and stir until melted.
Whisk together the cornstarch, Dijon, hot sauce and 1 teaspoon salt in a medium bowl, then gradually whisk in the evaporated milk. Add to the pot with the macaroni, along with the pasta cooking water, and cook over medium-high heat until bubbling. Take off the heat and add the cheese, stirring until melted.
Serve immediately either plain or with your desired stir-ins.