01 - Boil elbow macaroni in well-salted water until just al dente. Drain and set aside.
02 - In a large pot, melt butter over medium heat. Add diced onion and grated carrot; cook for about 4 minutes until vegetables are soft. Add minced garlic and cook for an additional minute.
03 - Sprinkle flour over the sautéed vegetables and stir continuously, cooking for 1–2 minutes to eliminate raw flour flavor.
04 - Gradually whisk in milk and vegetable broth, ensuring the mixture remains smooth. Bring gently to a simmer.
05 - Add dry mustard powder, salt, and freshly ground pepper. Reduce heat to low.
06 - Add shredded cheddar and mozzarella in portions, stirring until all cheese is fully melted and soup is silky.
07 - Return cooked macaroni to the pot. Heat gently for another 2–3 minutes, stirring, and adjust seasoning as necessary.
08 - Ladle hot soup into bowls and garnish with chives or green onions. Add bacon bits if desired.