Boil a pot of salted water and cook the elbow macaroni according to package directions until al dente. Drain thoroughly and set aside.

In a medium saucepan, melt 2 tablespoons of unsalted butter over medium heat. Whisk in the all-purpose flour and cook for 1 minute, stirring constantly.

Gradually pour in the whole milk while whisking continuously until the mixture is smooth. Continue to cook for 2-3 minutes, stirring until the sauce thickens.

Reduce the heat to low. Stir in the shredded cheddar cheese, mozzarella cheese, mustard powder, garlic powder, salt, and black pepper. Continue to stir until the cheese is fully melted and the sauce is smooth and creamy.

Add the cooked and drained macaroni to the cheese sauce. Stir gently to ensure every piece of pasta is evenly coated. Remove the saucepan from heat.

Lay out four of the flour tortillas. Evenly spread approximately 1/2 cup of the mac and cheese mixture over each of these tortillas, leaving a roughly 1/2-inch border around the edges.

Place a second flour tortilla on top of the mac and cheese filling on each of the prepared tortillas.

Heat a large skillet or griddle over medium heat. Melt a small amount of unsalted butter. Carefully place the assembled quesadillas onto the hot skillet.

Cook for 2-3 minutes per side, pressing down gently with a spatula, until each quesadilla is golden brown and crisp.

Remove the cooked quesadillas from the skillet. Allow them to rest for 1-2 minutes before cutting into wedges. Serve immediately while hot.