Cook pasta according to package instructions, drain and set aside. Keep the pasta water for later use.
Heat butter in a pot over medium heat until melted and foaming. Add mustard powder and mix.
Stir in Rainbow Evaporated Milk until combined, lower heat and allow to simmer.
With the heat on low, add the cheddar cheese, 2 tbsp at a time and stir until completely melted before adding more cheese. Repeat with the remaining cheeses.
Pour the cooked macaroni into the creamy sauce and stir until fully coated. If the cheese sauce is thick, add in the reserved pasta water, 1tbsp at a time until the desired consistency is reached. Serve immediately.