Broccoli Cheese Soup

This is a lovely recipe adapted from America's Test Kitchen. You'll notice the unusal addition of baking soda to this soup. The baking soda helps break down the broccoli—without it, the brocoli would have to cook for a good hour to be soft enough for our purposes. This hearty soup serves 6 to 8. I think this would also be really good over potatoes—baked or boiled or on grilled chicken.


Ingredients 


2 tablespoons butter 
2 pounds broccoli (about 4 crowns), florets cut into 1-inch pieces and the stems peeled and cut into quarter-inch pieces 
1 medium onion, roughly chopped 
2 large garlic cloves, minced 
1 1/2 teaspoons dry mustard powder 
Generous pinch of cayenne pepper 
1 teaspoon salt 
3 cups water 
1/4 teaspoon baking soda 
2 cups low-sodium chicken broth 
2 cups (or 2 large handfuls) fresh leaf spinach 
3/4 cup shredded reduced-fat sharp cheddar cheese 
3/4 cup shredded Parmigiano-Reggiano cheese 
Fresh ground black pepper, for serving 
Croutons or sliced bread, for serving 


Heat the butter in a large (I mean LARGE) Dutch oven over medium-high heat. When the foaming subsides, add the broccoli, onion, mustard, cayenne, garlic, and salt. Cook, stirring frequently for 6 minutes. Add 1 cup of water and baking soda. Reduce heat to medium-low and simmer for 20 minutes, or until the broccoli is very soft and broken down. Stir occasionally. Add chicken broth and 2 cups water and increase the heat to medium-high. When the soup begins to simmer, add in the spinach and let it cook for about a minute. Turn off the heat. Using an immersion blender, puree the soup until completely smooth. Stir in the cheeses and combine completely. Serve with a sprinkle of Parmigiano-Reggiano, black pepper, and croutons or bread.