Preheat the oven to 180°C. Score the chestnuts across the rounded side and roast for 40–50 minutes. 

While the chestnuts are cooking, finely slice the leeks and chop the garlic. Place them in a saucepan over medium-low heat with 3 tbsp of the olive oil and a pinch of salt. Sweat for around 20 minutes, stirring occasionally, until soft and sweet but not coloured. 

Cut the bread into 2cm cubes, toss with the remaining olive oil and spread over a tray. Place in the oven with the chestnuts and bake for 20–30 minutes, tossing every 10 minutes, until golden and crisp. 

Once the chestnuts are cooked, wrap them in a tea towel to keep them warm. Peel them while still hot, as the skins will come away more easily. 

Add the peeled chestnuts to the leeks, season generously with cracked pepper, then pour in the vegetable stock. Bring to a simmer and cook over medium heat for 10 minutes. Remove from the heat and leave to cool for 10 minutes. Blend until completely smooth using a blender. Taste and season with extra salt and pepper as needed.  

Divide among four bowls and top each with 1 tbsp sour cream, 1 tbsp chopped chives and a handful of golden croutons.