Wisconsin Cauliflower Soup

Ingredients

• 2 Tbsp butter
• 1 medium onion
• 1/4 cup all-purpose flour
• 1/2 tsp salt
• 2 cups milk
• 1 1/2 cups water
• 1 can chicken broth
• 1 head cauliflower
• 1 tsp Dijon mustard
• 1 cup sharp Cheddar cheese, shredded
• 1 cup Pepper Jack cheese, shredded