Step 1: Prepare the Cheese - Shred your sharp cheddar, mozzarella, and pepper jack cheeses (about 1 cup each, for a total of 3 cups). Set aside.
Step 2: Cook the Macaroni - Bring a large pot of lightly salted water to a boil. Add the elbow macaroni and cook until al dente (firm to the bite, usually 7–8 minutes). Drain well and set aside.
Step 3: Make the Roux - In a large pot or Dutch oven over medium heat, add the 3 tablespoons of unsalted butter. Melt completely. Stir in the 3 tablespoons of flour. Whisk constantly for 1–2 minutes until the mixture turns a light golden brown.
Step 4: Add the Milk Gradually - Warm the milk in the microwave for 1–2 minutes. Gradually pour the milk into the roux a little at a time, whisking vigorously after each pour until smooth and lump-free.
Step 5: Season the Sauce - Add the salt, pepper, onion powder, garlic powder, and ground mustard. Stir to combine. Cook over medium-high heat, stirring regularly, for 5–6 minutes until the sauce thickens and starts to bubble gently.
Step 6: Melt the Cheese - Reduce heat to low. Add the shredded cheeses one handful at a time, whisking until fully melted and smooth before adding more.
Step 7: Combine and Serve - Turn off the heat. Add the drained macaroni to the cheese sauce. Stir gently until the noodles are evenly coated.
