Preheat oven to 375F. Coat a 2.5-quart baking dish with non-stick cooking spray.
Cook pasta according to package directions; drain, reserving 1/2 cup pasta water.
Combine 1/4 cup evaporated milk and flour, stirring until smooth and blended.
In the pasta pot, cook the evaporated milk mixture, remaining evaporated milk, 2 cups cheddar cheese, Worcestershire, dry mustard, kosher salt, pepper and reserved pasta water over medium heat until the cheese is melted and the mixture is thickened, smooth and blended, stirring frequently.
Stir in the cooked pasta and toss until evenly coated. Transfer to the prepared baking dish. If you are preparing this recipe ahead, you can refrigerate it at this point until you are ready to top it and bake it, as per the instructions in the notes below.
Top with remaining 1/2 cup cheddar cheese.
Combine crushed crackers and melted butter and sprinkle on top.
Bake, covered, for 20 minutes. Uncover and continue baking for an additional 15 minutes or until the cheese is melted and the pasta is hot and bubbly.