01 - Cook macaroni in salted boiling water until just al dente. Drain and set aside.
02 - In a large pot, melt butter over medium heat. Add onion and carrot, cook until soft (about 4 minutes). Add garlic and cook for another minute.
03 - Sprinkle flour over the vegetables and stir to coat. Cook for 1-2 minutes to remove raw flour taste.
04 - Slowly whisk in milk and vegetable broth, ensuring no lumps remain. Bring to a gentle simmer.
05 - Add dry mustard, salt, and pepper. Reduce heat to low.
06 - Stir in cheeses, a handful at a time, stirring until fully melted and the soup is smooth.
07 - Add cooked macaroni. Heat gently another 2-3 minutes. Adjust seasoning as needed.
08 - Serve hot, garnished with chopped chives or crispy bacon bits if desired.