In a large soup pot, melt the butter over medium heat. Add the onions and cook until soft (approx 6-8 min.). Add the garlic and cauliflower pieces and stir occasionally, until cauliflower begins to soften and turn translucent (approx. 10 min. ).
Add vegetable broth and milk and bring to a boil. Once boiling reduce heat and continue to cook for approx.. 30 min. until the cauliflower is very tender.
Turn off the heat and let soup cool slightly. Use an immersion blender to puree the soup in the pot until it is smooth ( If you do not have an immersion blender you can also puree the soup in batches in a blender or food processor).
Turn on the heat to medium-low and sprinkle in cheese. Stir until the cheese is thoroughly melted and smooth. Season with salt and pepper to taste.
Top with croutons or crackers, a little extra shredded cheddar cheese, and chopped chives.
Serve with a crusty loaf of artisan bread for a lite but filling meal.