Fill a large saucepan with water and bring to a boil. Add in 1 pound elbow macaroni and cook to al dente, according to the package directions. Drain well. Drain well.
Meanwhile, in another large saucepan, melt ½ cup salted butter over medium heat. Once the butter is completely melted, whisk in ½ cup all-purpose flour, 1 ½ teaspoons onion powder, 1 ½ teaspoons ground mustard, 1 teaspoon salt, and ½ teaspoon white pepper. Cook for 2 minutes.
Slowly pour in 3 cups milk and whisk until smooth. Cook over medium-high heat, stirring constantly, for 3-5 minutes until the sauce starts to thicken. Turn off the heat and whisk in 8 ounces shredded sharp cheddar cheese until melted.
Pour cooked, drained pasta into the cheese sauce and stir well to combine. Serve hot.
