Bring broth to a simmer and add cauliflower. Cover pot with lid. Cook until tender, stirring/smashing occasionally, (about 5-6 mins). Drain cauliflower over a bowl to reserve broth and add cauliflower to food processor or blender. Add onion and salt. Return pot to stove and heat olive oil. Add garlic and saute on medium-low heat until fragrant and soft, 30-60 seconds. Add garlic and all oil from pan into cauliflower. Add 1/4 cup reserved broth, and cheeses. Process until smooth. Add salt and liquid to taste.