Line a baking sheet with baking parchment, spread the peanuts out in a single layer in the centre and set aside. Put the caster sugar and 3 tablespoons water in a small saucepan over a medium heat and cook for 2 minutes, stirring occasionally, until the sugar dissolved. Bring to the boil over a high heat and boil for 3–4 minutes until it turns a caramel colour. Immediately pour the caramel over the peanuts and spread it out slightly, using a lightly oiled palette knife. Leave to cool for 2 minutes, then carefully transfer the parchment to a cooling rack and leave to set in a cool place for 7–8 minutes. Meanwhile, put the cream in a bowl and whip, using an electric mixer, until soft peaks form, then set aside.