Bring a large pot of salted water to a boil. Add pasta and cook according to package directions.
Heat a saucepan or pot over medium heat. Add the butter. Once melted, whisk in the flour and cook 1 to 2 minutes until it just starts to bubble and turns a golden color.
Pour in the half and half and whisk continuously until smooth. Then add the dry mustard powder, garlic powder, black pepper, nutmeg, cayenne powder if using, and salt. Whisk together.
Reduce the heat to low and add all the cheeses. Whisk together until there are no more clumps and the sauce is completely smooth. Taste and adjust anything to your liking.
Once the pasta is done cooking, drain it and toss it into the sauce. Mix together and serve warm!