Start by melting the butter in a large saucepan. Add the onion and cook for roughly ten minutes or until tender and translucent.

Whisk in the flour, salt, and pepper until a paste is formed. Slowly stir in the milk, cream, water, and chicken broth. Make sure to stir one in at a time until fully incorporated.

Stir in the chopped cauliflower and bring to a boil. Reduce the heat to a simmer, cover, and cook 15 minutes or until the cauliflower is tender.

Using a hand blender, or transferring to a regular blender, blend until your soup is smooth.

Return the soup to a boil. Remove from the heat and stir in the mustard and two cheeses. Serve topped with bacon pieces and additional cheese.