In a large pot, add the pasta to salted, boiling water and cook accordingly to package directions, but removing 1 minute before al dente. Drain and set aside.
To the same pot, add the evaporated milk and heat over medium-low heat. Add the cheese in small batches and whisk until melted.
Stir in the ground mustard, garlic powder, paprika, and pepper. Add the pasta to the sauce and stir until the pasta is evenly coated. Transfer the mixture to a 9x13 baking dish.
In a small bowl, crush the Ritz crackers and add the melted butter. Stir together and sprinkle over the top of the mac and cheese.
Bake for 15 minutes or until golden brown and bubbly around the edges.
Use freshly grated cheese for the best melting quality.
Undercook the pasta slightly since it will finish cooking in the oven.
If you skip the baking step, let the mac and cheese sit for 10-15 minutes so the sauce has a chance to thicken up.
To freeze before baking - Pour the mac and cheese into an oven-safe dish. Let cool. Do not add cracker topping until you are ready to bake. Wrap tightly in aluminum foil and freeze for up to 2 months. Thaw in the refrigerator and bake, covered, at 350 degrees for 40-45 minutes or until hot and bubbly. Increase the oven temperature to 400 degrees and add the cracker topping. Bake for 5-10 minutes longer until the topping is golden brown.
To freeze after baking - Let cool. Cut into individual portions. Wrap in plastic wrap and aluminum foil and/or use a freezer-safe zipper top bag. Freeze for up to 2 months and thaw in the refrigerator. Portions can be reheated in the microwave or in the oven. The oven method will allow the cracker topping to regain its crispy texture.