Nifty!
And that recipe is called?
Melt your butter in a pot. Add flour. Cook until it kind of smells like short bread cookies and gets a toasty sandy colour.
Use equal parts of different cheeses that add up to around 1 cup. I've used a mix of smoked gouda, cheddar and mozzarella which was really good.
In creole cooking, we call that a roux.
In gumbos, I like to get my roux between a light tan to a milk chocolatey brown- the lighter it is, the more it can thicken. The darker it is, the more flavor it brings.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.