1. Peel the potatoes, parsnips, and onion, then dice them into 1 cm (½ inch) cubes

2. Melt the butter in a large heavy-bottomed pot over medium heat

3. Add the diced onion and cook for 4 to 5 minutes until softened and lightly golden

4. Stir in the potatoes and parsnips, cooking for another 6 to 7 minutes, stirring occasionally, until they begin to brown slightly

5. Pour in the vegetable broth, increase heat to high, and bring to a rolling boil

6. Reduce heat to low, maintain a gentle simmer at 90°C (195°F), and cook uncovered for 20 minutes, or until all vegetables are fork-tender

7. Remove from heat and blend the soup with an immersion blender until completely smooth

8. Return the pot to low heat and stir in the heavy cream

9. Warm gently for 3 minutes without bringing to a boil

10. Season with salt and white pepper to taste

11. Ladle into warmed bowls and top each serving with 15 ml (1 tbsp) sour cream

12. Garnish with 2 tbsp finely chopped fresh parsley

13. Serve with thick slices of toasted crusty bread on the side