In a dutch oven over medium heat, add bacon and cook until browned and crispy, about 7 minutes. Transfer bacon to a plate lined with paper towels; set aside.
In the remaining bacon drippings, cook the onion, carrots and celery, stirring occasionally, until tender, about 3-4 minutes. Add the garlic and cook for about 1 minute. Stir in cauliflower. Cook, stirring occasionally, until tender, about 3-4 minutes.
Stir in flour until lightly browned, about 1 minute. Gradually stir in chicken broth and milk, and heat, stirring constantly, until slightly thickened, about 3 or 4 minutes.
Bring to a boil; reduce heat and simmer until the cauliflower for about 12-15 minutes until cauliflower is tender; add salt and pepper and cayenne (if desired). You may have to add more milk if the chowder gets too thick.
Serve immediately, garnished with bacon and green onions, or any of your favorite toppings.