Preheat the oven to 140°C (275°F) (gas 1).
If using coffee granules, dissolve in 1 teaspoon of hot water and leave to cool.
Put the egg whites in a large bowl and whisk until just stiff.
Now gradually add the sugar, one tablespoon at a time, whisking constantly until the mixture becomes very thick and glossy.
Then sprinkle over the coffee and whisk until it has thoroughly mixed in.
Dab a little meringue on the corners of the baking sheets/trays which will prevent the baking parchment from slipping. Then line each sheet/tray, pressing the baking parchment down at the corners.
Spoon 4 mounds of meringue onto each baking sheet/tray, spacing them well apart.
Bake for 1 hour 15 minutes. The meringues should feel hard to the touch and lift off the parchment easily.
If you like your meringues crisp on the outside but chewy in the centre, then remove from the oven and leave to cool completely on a cooling rack. If you prefer them crisp all the way through, then leave in the oven, with the door slightly ajar, until the oven has become cold.
Meanwhile break the chocolate into small pieces, put in a heatproof bowl and set over a pan of just simmering water, making sure the bowl does not touch the water. Stir the chocolate until melted and smooth, then remove from the heat and leave until cold.
Drizzle the melted chocolate over the meringues.
Then leave in a cool place for the chocolate to set.