Preheat the oven to 350°F.
In a large cast iron skillet over medium heat, melt the butter.
Whisk in the flour until well combined to form a roux.
Slowly add the milk while constantly whisking, then the water. Whisk in the spices and mustard. Stir in the noodles. Turn the heat to medium-high and bring mixture to a boil.
Turn down the heat to low and let simmer for about 10-15 minutes (or more, as needed), until the noodles are cooked (a lot of the liquid will be absorbed, but some will remain).
Remove from heat and stir in the cheese until melted. If using, stir in the cashew cream.
Taste and add more salt and pepper, as desired.
Stir together the ingredients for the topping and sprinkle on top.
Carefully cover the pan tightly in foil. Place in the oven for 15 minutes, then carefully remove the foil and bake for 5 more minutes.
Serve immediately.