Watercress soup is silky, peppery, and quietly elegant: sweet potato and onions simmered in chicken broth with thyme until tender, then blended with a generous heap of fresh watercress. The sweet potato gives the soup body and sweetness while the watercress brings its signature pepper and spice. Ready in thirty minutes and beautiful poured into shallow bowls.
SERVES 4
Watercress can be hard to come by, so I snatch it up whenever I see it to make this soup. The watercress adds the perfect amount of pepper and spice to an otherwise sweet soup.
INGREDIENTS
3-4 tbsp/44-60 g butter
1 cup/150 g yellow onions, finely chopped
4 cups/950 ml Chicken Broth
1 medium sweet potato, peeled and diced
½ tsp sea salt
¼ tsp pepper
3 sprigs thyme
3 cups/540 g watercress
COOKING INSTRUCTIONS
Melt the butter in a heavy pot. Add the onions and sauté until translucent. Add the chicken broth, sweet potato, thyme, salt and pepper. Bring to a boil, reduce heat and simmer, partially covered, until sweet potato is very tender, about 20 minutes. Remove the thyme sprigs from the soup and discard.
Meanwhile, remove the leaves from the watercress and rinse. Add the watercress to the pot, cover, remove from heat and allow to cool. Put soup in a food processor and process until smooth. Return the soup to the pot and add more broth if it seems too thick. Adjust salt and pepper to taste and simmer until heated through.
CHEF’S TIP
I prefer Japanese sweet potato for this soup, as it is sweeter than most sweet potatoes.
Pro Tips
- Add the watercress off the heat and let it cool in the covered pot — this keeps the leaves' bright flavor and vivid green color instead of cooking them to army-drab.
- Japanese sweet potato is the chef's pick here; its chestnut-like sweetness outshines the orange-fleshed varieties in this particular soup.
- Simmer the sweet potato until genuinely tender (about 20 minutes) before blending — any firmness left will make the soup gritty.
- Thin the blended soup with extra broth a little at a time; it thickens as it stands, and you can always add more but never less.
- Use the leaves only — thick watercress stems add bitterness and fibrous texture to an otherwise silken soup.
Frequently Asked Questions
What can I use instead of watercress?
Baby spinach gives a milder soup, arugula a peppery one close to watercress's spirit. Watercress is worth seeking out when you can find it, though.
Can I make this soup ahead?
Yes — it keeps three days refrigerated. The color dulls slightly over time, so a quick reheat (never a hard boil) keeps it looking fresh.
Is watercress soup healthy?
Very — watercress is packed with vitamins and antioxidants, and the sweet potato adds fiber and beta-carotene. It's a light but genuinely nourishing bowl.
Can I use a blender instead of a food processor?
Either works. Blend in batches and don't overfill — hot soup expands dangerously once the motor starts.
Recipe Card
Ingredients
Method
- COOKING INSTRUCTIONS Melt the butter in a heavy pot.
- Add the onions and sauté until translucent.
- Add the chicken broth, sweet potato, thyme, salt and pepper.
- Bring to a boil, reduce heat and simmer, partially covered, until sweet potato is very tender, about 20 minutes.
- Remove the thyme sprigs from the soup and discard.
- Meanwhile, remove the leaves from the watercress and rinse.
- Add the watercress to the pot, cover, remove from heat and allow to cool.
- Put soup in a food processor and process until smooth. Return the soup to the pot and add more broth if it seems too thick.
- Adjust salt and pepper to taste and simmer until heated through. CHEF’S TIP I prefer Japanese sweet potato for this soup, as it is sweeter than most sweet potatoes.
