Cook the Pasta: Preheat oven to 350 degrees. In a deep pot or saucepan, bring chicken broth and water to a boil then add pasta and cook just shy of al dente (about 6-7 minutes) then drain. Save about ½ cup of pasta liquid to use later.
18 ounces uncooked pasta, 4 cups chicken broth, 4 cups water
Prepare the Cheese: Meanwhile, use a hand grater or food processor to shred the cheese. Mix all three cheeses together evenly and set aside.
2 cups mild cheddar cheese, 1 cup sharp cheddar cheese, 1 cup Gouda cheese
Make the Roux Cheese Sauce: Melt butter in a large saucepan or skillet over medium-high heat. Stir in the flour to start a roux then slowly whisk in the milk so that the mixture doesn't become lumpy. Reduce heat to medium then stir in the mustard, sea salt, white pepper, smoked paprika, and garlic powder. Once this mixture is thickened and starts to bubble, stir in two cups of the cheese, incorporating about one cup at a time.
6 tablespoons unsalted butter, 5 tablespoons all-purpose flour, 2 ½ cups evaporated milk, 2 teaspoons mustard, 1 teaspoon sea salt, ¼ teaspoon white pepper, ¼ teaspoon smoked paprika, ½ teaspoon garlic powder
Stir until the cheese sauce is smooth and uniform and all cheese is melted. It should be very thick but not stiff. If it is stiff, add some of the reserved pasta liquid, one spoonful at a time, to thin out the sauce a little.
Assemble the Mac & Cheese: Toss the drained pasta with the cheese sauce until it’s evenly coated then spread half the mixture into baking dish. Sprinkle half the remaining shredded cheese over top then add the rest of the pasta mixture, followed by the rest of the cheese.
Bake and Serve: Transfer the baking dish to the oven and bake, uncovered, for 40 minutes or until the mac and cheese is bubbly and the top is golden brown. Let it set for about 10 minutes before serving.