Smoky Gouda Cauliflower Soup

1 medium white onion, chopped
1/2 c. butter, split in half
1 large head Cauliflower, chopped
1/4 c. flour
2c. heavy cream
2 14 1/2 oz.  cans chicken broth
1 1/2 c. smoked gouda cheeses, grated
1/2 c. pepper jack cheese, grated
1/2 c. cheddar cheese, grated
1/2 teas. season salt
2 teas. dijon mustard
1 teas. yellow mustard
pinch cayenne pepper

In large pot, melt 1/4 c. butter and cook onions until translucent. Add broth, spices and cauliflower. Cook app. 25 minutes or until vegetables are tender. Puree mixture.
In separate pot, melt remaining butter, whisk in flour and cook until bubbly, remove from heat. stir in cream and cheeses. Pour milk mixture into cauliflower mixture's pot. Heat until cheese melts and soup thickens and constitutes.
Adjust spice to taste.