Mornay Sauce

In a small saucepan set to medium heat, melt butter completely and then add the flour. Whisk continuously until it starts to bubble, about one minute. Continue whisking and slowly pour in the milk. It will get very thick at first, but as the milk is added, it will thin out.

Reduce heat to low and continue whisking, allowing the sauce to thicken. If there are any lumps, whisk them thoroughly until they've smoothed out. Add the salt, pepper and nutmeg.

Keeping the heat on low, add the cheese a handful at a time, allowing it to almost melt entirely before adding the next bit. Taste for seasoning, then remove from heat. Serve immediately.