Potato soup with chorizo

Method

1. Melt the butter in a pan and add the potatoes and onion. Season, stir well, cover with a lid and sweat over a gentle heat for 10 minutes.
2. Add the chicken or vegetable stock, bring to the boil, cover again, and simmer for another 10 minutes, until the vegetables are soft. Add the milk, then blitz with a hand-held blender, until smooth.
3. Make the parsley pesto. Put all the ingredients, except the olive oil, into a food processor and whizz to a textured purée. Add the oil and a good pinch of salt and whizz briefly to a coarse paste. Spoon into a sterilised jar, cover with 1cm oil and store in the fridge for up to 2 weeks. Cover with more oil after each use.
4. Heat the olive oil in a large frying pan. Add the chorizo slices and fry for 30 seconds each side, until crisp and the oil has run out into the pan. Lift the chorizo onto kitchen paper to drain briefly. Reserve the rich, amber-coloured oil.
5. Divide the hot soup between warm bowls, and swirl 1 teaspoon of pesto into each bowl. To serve, top each soup with 3 chorizo slices and a little of the reserved chorizo oil.