01 - Cook macaroni in salted boiling water until al dente. Drain thoroughly and set aside.
02 - Melt butter in a large pot over medium heat. Add onion and carrot, cooking until softened, approximately 4 minutes. Add minced garlic and cook for 1 minute until fragrant.
03 - Sprinkle flour over the vegetables, stirring constantly to coat. Cook for 1-2 minutes to eliminate raw flour taste, creating a light roux.
04 - Gradually whisk in milk and vegetable broth, ensuring smooth incorporation without lumps. Bring mixture to a gentle simmer while stirring.
05 - Add dry mustard powder, salt, and pepper. Reduce heat to low to maintain gentle simmer.
06 - Gradually stir in shredded cheeses, one handful at a time, allowing each addition to melt completely before adding more. Continue stirring until fully incorporated and soup is silky smooth.
07 - Add cooked macaroni to the soup. Heat gently for 2-3 minutes until pasta is heated through. Taste and adjust seasoning as needed.
08 - Ladle hot soup into bowls. Garnish with chopped chives or green onions. Add crispy bacon bits if desired.