Melt butter in a medium sized saucepan
. When it's hot, add flour and whisk it well; keep whisking while it cooks for 2 minutes or so, but keep the heat on low-medium and don't let it burn. Add milk slowly and keep whisking, it'll start to thicken. Once you have it all stirred in (again, keep whisking and don't have your heat too high or it will stick and burn), add the cheese. Keep whisking as it melts and add some pepper and plenty of sea salt
to give it a great taste – do some taste testing to get it right -- add more cheese too, if desired. (This cheese sauce is also great on steamed veggies and it's the same sauce I use for my ham & escalloped potatoes
.) If it gets too thick, add a little more milk and whisk some more.