But the beauty of this soup — and of soup in general — is its flexibility. I've made it with vegetable stock, chicken stock and plain water. I've skimped on the broccoli and used more potato. I've started with onion or green garlic in place of the leek. And every rendition is good: creamy, bursting with broccoli, with a sharp edge of cheddar peeking out.
Roasted Broccoli & Cheddar Soup
2 tablespoons oil, divided
1 leek, washed
1 medium waxy potato
1 bunch broccoli (about 1 1/2 pounds)
6 cups vegetable stock, chicken stock or water
1 cup grated extra-sharp cheddar cheese
Salt and pepper
Crème fraîche or yogurt (optional)
Preheat the oven to 425°F. Thinly slice the white and light green portion of the leek. Heat 1 tablespoon of oil in a large pot over medium heat and add the sliced leek. Cook, stirring occasionally, until the leek is soft. While the leek cooks, peel and chop the potato into 1-inch chunks. Add the stock and potato to the pot and bring the mixture to a boil.
While the stock is coming to a boil, chop the broccoli into florets and spread onto two sheet pans. If the excess broccoli stalks are tender and tasty, they can be peeled and added to the pans. Drizzle the remaining tablespoon of oil over the broccoli, sprinkle with a little salt and put the pans in the oven. Roast for 5 minutes. Stir the broccoli and return to the oven for 5 more minutes.
Once the stock is boiling, add the broccoli and bring to boil again. Simmer until both the potatoes and broccoli pieces are tender when pierced with a fork, about 5 minutes. Remove from the heat. Puree soup with an immersion blender or in batches with a regular blender. Add the cheese and stir until it has melted and incorporated into the soup. Taste soup and adjust the seasoning. If you are not serving the soup with crème fraîche or yogurt, add a squeeze of lemon. Serve topped with a small dollop of crème fraîche or yogurt, or a grind of fresh pepper.