In a large pot or cast irons skillet over medium heat, melt the butter and add in the flour. Whisk together for about 1 minute to fully cook the flour. Add in the cream cheese and continue to whisk together while slowly adding the first cup of milk in about 4 additions whisking the sauce together until combined between each pour. While continuing to whisk, add in the rest of the milk. While the sauce is thickening, add the seasoned salt, smoked paprika, brown sugar, white pepper, and nutmeg. Once the sauce has thickened (about 5 minutes) mix in the shredded cheddar and Monterey Jack cheese and stir until smooth. Reduce heat to low.

Boil pasta to al dente and add to the cheese sauce. Reserve about a cup of pasta water. Take off the heat and stir together. The sauce will be loose but will thicken as it cools. Add the pasta water as needed to keep a creamy sauce.