Lemon ganache

Makes: about 650 g (1 lb 7 oz) to fill and cover one 18 cm (7 in) round cake

Preparation time: 15 minutes

Cooking time: 5 minutes

Chilling time: at least 1 hour

225 g (8 oz) white chocolate, broken into pieces

100 ml (3½ fl oz) lemon juice

finely grated zest of 1 lemon

Put the chocolate in a heatproof bowl set over, but not touching, a saucepan of gently simmering water, and stir occasionally, until melted, about 5 minutes. Meanwhile, pour the lemon juice into a small saucepan and bring to the boil. Remove the bowl of chocolate from the heat, pour the lemon juice over it and stir until well combined. Add the lemon zest and combine until the ganache is smooth. Cover with plastic wrap and chill immediately in the refrigerator for at least 1 hour before using.