Preheat the oven to gas 2, 150°C, fan 130°C. Beat the egg whites with a pinch of salt until they form soft peaks, then gradually add the sugar and vanilla extract, constantly beating until the mixture is firm and glossy. Transfer to a piping bag with a large plain nozzle.
Pipe 16-20 ghosts onto a baking tray lined with nonstick baking paper. The meringues will increase in size as they dry out. Reduce the oven temperature to 100°C and bake for about 2 hours until the meringues are crisp on the outside, leaving the oven door open a crack. The meringues should not brown. If necessary, reduce the oven temperature to 80°C and let them dry out for a little longer. Turn the oven off and leave the meringues in there until is has cooled.
Melt the chocolate over a bain-marie and put into a freezer bag. Cut off a corner to make a tiny hole and pipe two eyes on each ghost.
Leave to dry before serving.
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