1 large (US extra-large) egg white
225g/8oz/1 cup golden caster (superfine) sugar
a pinch of cream of tartar
1 Put the egg white in a clean, grease-free bowl and whisk until it forms stiff peaks.
2 Put the sugar, 4 tbsp water and the cream of tartar in a pan and heat gently, stirring, until the sugar dissolves. Bring to the boil and boil until the sugar syrup reaches 115°C/239°F on a sugar thermometer. Or drop a little into cold water – when it forms a soft ball that you can squash between your finger and thumb, it’s ready.
3 Remove from the heat and when the bubbles subside, pour on to the egg white in a thin stream, whisking constantly, until thick and white. Set aside to cool slightly.
4 When it is almost cold, pour quickly over the cake and spread evenly with a palette knife.
5 This makes enough to cover the top and sides of a 20cm/8in cake.