Prep work: Gather all ingredients. Grate the cheeses, measure the butter, flour, and heavy whipping cream. You do not want your sauce waiting on you.
3 tablespoons butter, 1 tablespoon flour, 1 cup shredded mild cheddar cheese, 1 cup shredded smoked gouda, 1 cup heavy whipping cream
Pasta: Prepare 2 cups of pasta in a 2-quart saucepan with enough water to cover the pasta by 2". I use 1 teaspoon of salt for every 3 cups of water. Bring the water to a boil. Add salt and stir. Then, add pasta and cook for 7-9 minutes or until desired tenderness. Reserve ½ cup pasta water before draining.
2 cups dry elbow macaroni, 1 teaspoon sea salt per 3 cups of water to boil pasta
Butter: Melt the butter in a small saucepan over very low heat, stirring to prevent burning or browning.
Roux: As soon as the butter is melted, whisk in the flour to make a roux. Continue to whisk over low heat 1 to 2 minutes to cook the flour. This mix will get frothy and should remain a pretty yellow color. If the mix turns brown, abort and start over. It's better to do this now, than to end up with a burnt flour taste in your sauce.
Cream: While continuing to whisk the roux, slowly pour in the heavy whipping cream. Over medium low heat, mix until well combined, slightly thickened and bubbly. This will make a smooth, white sauce that will be runny but coat the back of a spoon.
Cheeses: Next, add the cheeses; reduce the heat back to low and stir until the cheese is completely melted and the sauce is smooth and creamy.
Finishes touches: Stir in salt, black pepper, dried mustard and nutmeg.
1/4 teaspoon sea salt to flavor sauce, 1/8 teaspoon ground black pepper, 1/4 teaspoon dry mustard, 1/4 teaspoon ground nutmeg
Pasta water: Add the pasta water and combine. The sauce will seem soupy and too runny, but once it's added to the pasta it will all thicken up.
1/4 cup pasta water
Combine: Combine the sauce with well drained cooked pasta.
Enjoy!