It seems counterintuitive, but cooking the daylights out of the broccoli is the key to this soup’s sweet, nutty vegetable flavour. Our first step was to call for a full 2 pounds of broccoli.
Following a technique from renowned California chef Alice Waters, we sauteed the broccoli in a little butter, added a cup of water, and let it cook until it was very soft and nutty and sweet. We discovered that adding just a pinch of baking soda with the water accelerated the braising time by helping to break down the cell walls of the broccoli.
Adding fresh baby spinach right before pureeing ensured that our soup had a bright colour and it also enhanced the vegetable flavour. As for the cheese, a mix of sharp cheddar and nutty Parmesan gave the soup enough cheesy flavour and richness that we didn’t need to use any cream.
Start to finish: 1 hour, 15 minutes
2 tablespoons unsalted butter
2 pounds broccoli, florets cut into 1-inch pieces, stalks peeled and sliced 1/4 inch thick
1 onion, chopped coarse
2 garlic cloves, minced
1 1/2 teaspoons dry mustard powder
Pinch cayenne pepper
Salt and pepper
3-4 cups water
1/4 teaspoon baking soda
2 cups chicken or vegetable broth
2 ounces (2 cups) baby spinach
3 ounces sharp cheddar cheese, shredded (3/4 cup)
1 1/2 ounces Parmesan cheese, grated fine (3/4 cup), plus extra for serving
Melt butter in Dutch oven over medium-high heat. Add broccoli, onion, garlic, dry mustard, cayenne, and 1 teaspoon salt and cook, stirring frequently, until fragrant, about 6 minutes. Add 1 cup water and baking soda. Bring to simmer, cover, and cook until broccoli is very soft, about 20 minutes, stirring once during cooking.
Add broth and 2 cups water and increase heat to medium-high. When mixture begins to simmer, stir in spinach and cook until wilted, about 1 minute. Transfer half of soup to blender, add cheddar and Parmesan, and process until smooth, about 1 minute. Transfer soup to medium bowl and repeat with remaining soup. Return soup to pot, place over medium heat and bring to simmer. Adjust consistency of soup with up to 1 cup remaining water. Season with salt and pepper to taste. Serve, passing extra Parmesan separately.