Whisk the egg whites and cream of tartar in a grease-free bowl until stiff, then gradually whisk in the sugar, 1 tablespoon at a time, until the mixture thickens. Fold in the cocoa powder, almonds and almond extract with a metal spoon until evenly combined.
Spoon the mixture into a piping bag fitted with a large star nozzle and pipe 2.5 cm (1 inch) rosettes onto 2 large, lined baking sheets (you should have 40–50 rosettes, depending on the size).
Bake in a preheated oven, 150°C (300°F), Gas Mark 2, for 15 minutes until the biscuits are just set. Remove from the oven and leave to cool completely on the baking sheets.
Melt the chocolate with the cream in a bowl over a pan of simmering water (see