Equipment
Ingredients
Soup Base
- 30 g unsalted butter
- 200 g leeks (whites and light green parts only), washed and sliced
- 250 g yukon gold potatoes, peeled and diced 1cm
- 600 ml chicken stock
- 300 g watercress, thick stems removed
- 100 ml heavy cream, 35% fat or higher
Garnish
- 60 g crème fraîche
- 20 g caviar
- salt
- white pepper
Nutrition (per serving)
Nutrition is estimated per serving. Nutrients without complete source data are omitted.
Full nutrition
- Calories
- 488 kcal
- Protein
- 13 g
- Carbohydrates
- 67 g
- Fat
- 20 g
- Fiber
- 5 g
- Sugar
- 7 g
- Sodium
- 760 mg
- Saturated Fat
- 11 g
- Trans Fat
- 0 g
- Monounsaturated Fat
- 5 g
- Polyunsaturated Fat
- 1 g
- Cholesterol
- 80 mg
- Potassium
- 1017 mg
- Calcium
- 208 mg
- Iron
- 2.7 mg
- Magnesium
- 89 mg
- Phosphorus
- 216 mg
- Zinc
- 0.7 mg
- Vitamin A
- 344 mcg
- Vitamin C
- 41 mg
- Vitamin D
- 0.6 mcg
- Vitamin E
- 1.9 mg
- Vitamin K
- 212 mcg
- Vitamin B6
- 0.7 mg
- Vitamin B12
- 1.1 mcg
- Thiamin
- 0.26 mg
- Riboflavin
- 0.24 mg
- Niacin
- 2.6 mg
- Folate
- 60 mcg
- Water
- 147 g
Sources: Aggregated Public Data, USDA FoodData Central
Method
Prepare an ice bath in a large bowl. Bring a medium pot of salted water to a rolling boil.
Blanch the watercress in the boiling water for exactly 30 seconds until bright green, then immediately plunge into the ice bath to stop the cooking and set the chlorophyll. Drain well and squeeze out excess water.
In the heavy-bottomed pot, melt the butter over medium-low heat. Add the sliced leeks and a pinch of salt. Sweat gently for 8-10 minutes without browning.
Add the diced potatoes and stock to the pot. Bring to a simmer, cover, and cook for 15-20 minutes until the potatoes are completely tender and falling apart.
Remove the pot from heat. Add the blanched, squeezed watercress to the hot potato mixture. Transfer to a blender and puree on high speed until extremely smooth.
Pass the soup through a fine mesh sieve (chinois) back into the cleaned pot. This removes any fibrous watercress stems and ensures a Michelin-level silky texture.
Stir in the heavy cream and gently reheat to serving temperature (approx 75°C/167°F). Season with salt and white pepper, keeping in mind the saltiness of the caviar garnish.
Ladle the soup into warmed bowls. Place a dollop of crème fraîche in the center, create a small well in the cream, and top with a teaspoon of caviar. Serve immediately.
Chef's Notes
- Use white pepper instead of black pepper to maintain the soup's pristine green appearance without visible black specs.
- The potato variety matters; Yukon Gold (or similar waxy-starchy hybrid) provides creaminess without the gluey texture of pure russets or the hardness of waxy reds.
- Serve with a glass of Champagne or a crisp Chablis to cut through the richness of the cream and complement the brininess of the caviar.
- If the soup is too thick after blending, thin it with a splash of water or milk rather than more stock to preserve the pure watercress flavor.
Storage
Refrigerator: 2 days — Color will darken from bright green to olive upon reheating; flavor improves.
Freezer: 1 month — Texture may become slightly grainy due to potatoes and cream; blend again upon reheating.
Reheating: Gently reheat on low on the stove to 70°C/158°F. Do not boil, or the soup will lose its vibrant color and the emulsion may split.
Troubleshooting
Soup is olive green or brown instead of bright green
Cause: The watercress was overcooked or the soup was kept hot for too long, causing chlorophyll degradation.
Fix: Add a handful of raw spinach leaves and re-blend/strain to restore color without altering flavor significantly.
Prevention: Strictly adhere to the blanch/shock method and add watercress only at the blending stage.
Cultural Context
Watercress soup (Potage Cressonnière) is a staple of French bourgeois cuisine, traditionally thickened with potato. By refining the texture through a chinois and adding caviar, this rustic dish is transformed into 'Potage Germiny,' a style of soup often associated with Parisian fine dining in the early 20th century.
