Prepare the pasta according to the directions on the box. I like to start the pot of water boiling, then start on the cheese sauce. This usually works out well, so that they are both done at the same time.

To make the cheese sauce, start by melting the butter in a saucepan over medium heat.

Once melted, whisk in the flour and mustard. Cook this for a bit, maybe a minute, stirring the whole time.

Then slowly and carefully, pour in the milk, whisking quickly the whole time. It will sputter and spatter, just keep whisking. The lumps will go away too as long as you keep whisking. That is the key to this recipe – do not let it set, even for a minute, it will burn (yes, I know this for a fact! J) – keep stirring and using a whisk is the best way to make sure it’s all even with no lumps.

So, you stir, and stir, and stir some more until you see it becoming thick and creamy.

When you just start to see big bubbles pop through the top (and you think your arm will fall off from all that whisking), it’s time to stir in the cheese. Keep stirring it in until all the cheese is melted and incorporated into the sauce. Season with salt and pepper to taste.