Chestnut, mushroom and thyme soup

Method

1. Put the porcini in a heatproof jug, pour over 300ml just-boiled water and leave to soak for 20 minutes.

2. Meanwhile, melt the butter with the oil in a large saucepan over a medium heat. Add the onions and celery with a pinch of salt and cook, stirring now and then, for 10 minutes until soft and translucent.

3. Turn the heat up to medium-high and add the chestnut mushrooms a couple of handfuls at a time, letting each batch wilt before adding the next. Cook, stirring often, for 12-15 minutes until the liquid they release has evaporated and they are golden. Add the garlic and thyme for the last 2 minutes.

4. Lift the porcini out of the jug, chop finely and add to the pan. Pour in the soaking liquid, leaving the last gritty tablespoon behind in the jug, then add the chestnuts and stock.

5. Bring to the boil, then lower the heat, partly cover and simmer for 20 minutes until the chestnuts are soft enough to crush with a spoon.

6. Take the pan off the heat and blend with a stick blender until very smooth, or blend in batches in a jug blender filled no more than halfway, holding the lid down with a folded tea towel. Stir in the vinegar, season well with salt and pepper and add a splash of hot water if it is too thick.

7. Ladle into bowls and top each with a spoonful of crème fraîche, if using, and a few thyme leaves. Leave the rest of the soup to cool before portioning for the freezer (see tips).

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