First, make the ice cubes. Bring 75ml water, the malt vinegar and sugar to the boil. Add the mint leaves and set aside to steep for 10 mins. Strain into a jug, then pour into 12 holes of an ice cube tray and freeze until solid.
In a heavy-based saucepan, heat the butter until foaming, add the bacon and fry until crispy. Remove using a slotted spoon and set aside. Add the onion to the pan and cook until soft, about 10 mins. Add the sugar and 400ml water, bring to the boil, then add the frozen peas and mint. Bring back to the boil for 1 min, then remove from the heat and leave to cool a little. Pour the soup into a blender and blend until smooth. Pass through a fine sieve into a bowl (see tip below). Taste and season, then cover with cling film and chill until ready to serve.
Chop the crispy bacon into small bits. To serve, mix the bacon with the fresh peas and rapeseed oil in a bowl. Ladle the soup into your dishes and add the ice cubes (if you like, you can crush them a bit too). Top with the bacon
and peas, and scatter over a few mint leaves.