- With the rack in the middle position, preheat the oven to 400°F (200°C).
- On a non-stick or parchment paper-lined baking sheet, toss the cauliflower with 2 tbsp (30 ml) of the oil. Season with salt and pepper. Bake for 25 minutes or until golden, stirring halfway through.
- In a pot over medium heat, soften the leek in the remaining oil. Season with salt and pepper.
- Add the roasted cauliflower, potato and broth. Bring to a boil. Simmer over medium heat for 15 minutes or until the potato is cooked through.
- Meanwhile, in a small bowl, combine the cream and egg yolks.
- Remove the pot from the heat. Using a hand blender, purée the soup until smooth. Add the cream mixture. Return the pot to the heat and simmer for 2 to 3 minutes, stirring constantly. Strain the soup through a sieve. Adjust the seasoning.
- Meanwhile, in a bowl, using a hand blender, combine the herbs with the oil and lemon juice. Season lightly with salt.
- Serve the soup in bowls. Drizzle with cream and the herb oil. Garnish with the radishes.
The soup can be reheated over low heat while stirring frequently. Do not bring it to a boil, otherwise the egg yolks could coagulate.