Add butter to pot and melt.
Add chopped onions and garlic into pot and saute for about 5 minutes or until beginning to brown.
Lower heat and add flour and stir.
Slowly add water, broth, salt and chopped cauliflower.
Simmer covered until cauliflower is fork tender, which takes about 15 minutes.
Remove from heat and add milk.
Transfer contents into a blender in comfortable batches and blend until creamy smooth. I also add my pepper jack cheese into the blender, so the pepper flakes in the cheese are also blended up.
Pour soup back in pot and add mustard, sharp cheddar cheese and pepper. Stir together until cheese is melted and soup is smooth.
Serve immediately, or warm when ready to eat.
Top with some garnish, cheese, or just gobble it up silky smooth. Oh, so very good!