Preheat oven to 180C. Whisk eggwhites, sugar and a pinch of salt in a heatproof bowl over a saucepan of gently simmering water until mixture is warm to touch (4-5 minutes). Transfer to the bowl of an electric mixer and whisk on high speed until firm peaks form, then fold through cocoa, vanilla and almond.
Spoon mixture into a piping bag fitted with a 12mm-plain nozzle, pipe 5cm-mounds onto a large baking paper-lined tray and bake until dry (25-30 minutes). Transfer to a wire rack to cool. Drizzle chocolate over rochers and stand until set. Rochers will keep in an airtight container for up to 3 days.
Note Vanilla-bean paste is available from select delicatessens and supermarkets.