Whisk the egg white and sugar together until blended. Sift the flour and cocoa powder into the bowl. Stir in the cream and butter.
Line 4 baking sheets with nonstick baking paper. The biscuits will be baked in 4 batches. Place the first 4 dessertspoons, spaced well apart, on a sheet and spread lightly with the back of a spoon. Bake in a preheated oven, 220°C (425°F), Gas Mark 7, for 4 minutes until the biscuits have spread and the edges are beginning to darken.
Remove from the oven and leave for 30 seconds. Using a palette knife, lift each biscuit from the paper and wrap them around the handles of wooden spoons until set. Carefully twist the biscuits off the spoons and transfer them to a wire rack. Bake 3 more batches.
Melt the chocolate in a bowl over a pan of simmering water (see