To make the meringue, preheat the oven to gas 1, 140°C, fan 120°C.
Line a large baking sheet with nonstick baking paper and draw a 20cm circle in pencil. Turn the paper over so the pencil won't rub off on the food.
Using an electric whisk, beat the egg whites, caster sugar and a pinch of salt in a clean, dry mixing bowl on high speed for 4 mins, or until stiff peaks form.
Add the icing sugar and gently whisk until incorporated. Increase the speed and whisk for 3 mins, or until thick, stiff and glossy. Add the cocoa and whisk briefly to mix.
Using the pencil circle as a guide, spoon the meringue onto the paper in a nest shape with a deep hollow in the centre, keeping the sides tall. Bake for 1 hr 30 mins, or until slightly cracked in places and firm to the touch. Turn the oven off, pop the door slightly ajar and leave the meringue inside to cool
Meanwhile, make the chocolate curls. Using a vegetable peeler, scrape the chocolate from the flat, long side of the chocolate bar to make long curls. Set aside until needed.
In a mixing bowl, lightly whip the cream and fromage frais with the icing sugar to soft peaks. Spoon into the centre of the cooled meringue and top with the mini eggs and chocolate curls. To serve, dust with a little extra icing sugar.
Freezing and defrosting guidelines Freeze meringue only. Bake according to the recipe but stop before adding decoration or icing if called for. Allow to cool completely. Wrap well in clingfilm and tin foil (to prevent freezer burn) and freeze for up to 3 months. Loosen the tin foil and clingfilm but leave to defrost in packaging at room temperature for several hours before serving. If you wish to add icing or decoration, add them after the baked goods have fully defrosted and are at room temperature.