Here's how it goes...(Adapted from Martha Stewart's Macaroni and Cheese recipe)
I start off by pouring 2.75 cups milk (sometimes I use nonfat, sometimes 2%, whichever we have more of...or sometimes mix the two) into a glass measuring cup, and put it in the microwave for a minute or two. Just to warm it up...it helps with the mixing process later on.
After doing this, I put a large pot of water over high heat. Once it's boiling, I add in my macaroni noodles (2 cups of dry elbow mac). I cook according to package directions, but subtract one or two minutes from the cooking time. They'll continue cooking in the oven later.
Then, melt 3 tablespoons butter in a high-sided skillet (I used a large saucepan this time) over medium heat, just until it starts to bubble. You don't want to let it brown.
Once the butter bubbles, whisk in 1/4 cup flour.
Whisk until it starts to bubble, just about one minute. This is just to get rid of the raw flour taste.
Then, VERY slowly, start adding in your warm milk, whisking the whole time. If you add the milk in too fast, you'll have lumps of flour/butter. Pouring it in slowly (I do little bits at a time, while whisking in between) helps ensure a smooth sauce.
Once all of the milk is incorporated, and you have no lumps, let it simmer for about ten minutes, stirring (or whisking) every few minutes.
In the meantime, shred your cheeses. You'll need 4 ounces of Gruyere, and 8 ounces of cheddar. I shred my own Gruyere, but use pre-shredded Tillamook medium cheddar from Costco...I always have it on hand, so that's what I use.
After about ten minutes, the sauce will have thickened nicely and will start bubbling a bit.
Around this same time, your macaroni noodles should be ready to be drained.
Then it's time to add in your spices. Salt, pepper, cayenne, and fresh ground nutmeg to taste. If I had to guess, I'd say it's about an eighth of a teaspoon of each...maybe less cayenne. Stir those all in.
Turn the heat off, and add in your cheeses, leaving a bit of each kind of cheese out for the topping.
Stir your cooked macaroni noodles into the cheese sauce.