Bring a large pot of salted water to a rolling boil. Add elbow macaroni and cook until al dente, about 7-8 minutes. Strain and set aside.

Melt 2 tablespoons of unsalted butter in a saucepan over medium heat. Whisk in 2 tablespoons of flour and cook for 1 minute until smooth.

Gradually pour in 1 cup of whole milk while whisking continuously. Cook until it thickens and bubbles gently for 2-3 minutes.

Remove from heat, stir in 1 cup of sharp cheddar cheese and 1 cup of mozzarella until melted. Add mustard powder, garlic powder, salt, and pepper.

Fold cooked macaroni into the cheese sauce until well coated.

Lay a tortilla flat, spread mac and cheese filling over half, and fold to form a half-moon. Repeat with remaining tortillas.

Melt 1 tablespoon of butter in a skillet over medium heat. Cook quesadillas for 2-3 minutes on each side until golden brown.

Let the quesadillas rest for 1-2 minutes, then cut into wedges and serve hot.