Begin by bringing a large pot of salted water to a rolling boil. Add elbow macaroni and cook according to package instructions until al dente, usually about 6-8 minutes. Drain the pasta and set it aside.

In a large pot, melt 3 tablespoons of unsalted butter over medium heat. Add the chopped onion and sauté for about 5 minutes until translucent. Add minced garlic and cook for another minute.

Sprinkle 2 tablespoons of all-purpose flour and 1 tablespoon of cornstarch over the sautéed mixture. Stir continuously for 1-2 minutes until lightly golden.

Gradually whisk in 4 cups of chicken or vegetable broth and 1 cup of milk, stirring until no lumps remain. Bring to a gentle simmer.

Add 1 teaspoon of salt, ½ teaspoon of black pepper, 1 teaspoon of smoked paprika, and ½ teaspoon of mustard powder. Stir well.

Slowly incorporate 2 cups of shredded sharp cheddar cheese into the soup, stirring until melted and smooth.

Mix in ½ cup of grated Parmesan cheese until creamy. If using, fold in 1 cup of frozen peas.

Gently fold the cooked elbow macaroni into the cheese sauce, ensuring each piece is coated.

Ladle into bowls, garnishing with chopped parsley. Serve immediately.