Wisconsin Cauliflower Soup

This is a copy-cat recipe for Zupa's Wisconsin Cauliflower Soup:

2 Tbsp. butter
1 medium onion, chopped
1/4 c. flour
1/2 tsp. salt
2 cups milk or cream (I used half-n-half)
1 can (13 oz.) chicken broth
1 head (2 1/2 lbs.) cauliflower, cut into 1" pieces
1 cup Sharp Cheddar Cheese
1 cup Pepper Jack Cheese ( I doubled this, cuz we love it)

In a 4-qt. saucepan, melt butter over medium heat. Add onion & cook til golden, about 10 min. stirring occasionally. Stir in flour & salt; cook 2 min. stirring frequently. Gradually stir in milk or cream, chicken broth, and 1 1/2 cups of water. Add cauliflower & heat to boiling over high heat. Reduce to low; cover & simmer until cauliflower is tender, about 10 min. Use an immersion blender to blend till very smooth. (Can use normal blender, too, just do in small batches.) Remove saucepan from heat; stir in cheese. (It is not necessary to blend, it tastes just as good if you don't.) Garnish with extra cheese & a sprinkle of parsley.