Melt your butter in a pot. Add flour. Cook until it kind of smells like short bread cookies and gets a toasty sandy colour.
In creole cooking, we call that a roux. I sometimes use butter, lard or bacon grease for certain dishes, but most o the time, I use some kind of plant based oil.
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.
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.
AMEN! Mixing cheeses to get different textures and flavors is a an important culinary weapon. I must have a dozen different cheeses in my fridge right now- smoked gouda, truffle gouda, blue castello, cambozola, Stilton, Boursin, swiss, Parrano, truffle gouda, Monterrey Jack, American (both Kraft singles- for my Dad- and the real stuff for every other use), havarti, butterkäse, port wine, cahill, herbed D’Affinois, belletois, and so forth.
Even with simple things like grilled cheese sandwiches, I use mixes.