01 - Boil macaroni in salted water until al dente. Drain thoroughly and set aside.
02 - Melt butter in large pot over medium heat. Add onion and carrot; sauté 4 minutes until softened. Add garlic; cook 1 minute until fragrant.
03 - Sprinkle flour over vegetables, stirring constantly to coat. Cook 1-2 minutes to eliminate raw flour taste.
04 - Gradually whisk in milk and vegetable broth, ensuring smooth incorporation. Bring mixture to gentle simmer.
05 - Stir in dry mustard powder, salt, and pepper. Reduce heat to low setting.
06 - Add cheeses in small batches, stirring continuously until completely melted and soup achieves velvety consistency.
07 - Fold cooked macaroni into soup. Heat gently 2-3 minutes until pasta is warmed through. Adjust seasoning to preference.
08 - Ladle soup into bowls and garnish with chopped chives. Serve immediately while hot.