Draw 3 circles of 20cm/8in each on sheets of baking parchment, turn over and place on 3 baking sheets.Preheat the oven to 140℃ (120℃ fan)/275°F /gas mark 1.
Whisk the egg whites until standing in soft peaks, then gradually whisk in half of the caster sugar adding a tablespoon at a time. Continue whisking until he mixture is very stiff and glossy.
Carefully fold in the remaining caster sugar with a metal spoon or spatula, followed by cornflour and grated chocolate .
Spoon the meringue into a piping bag fitted with a large star nozzle. Pipe rosettes in a circle using the drawn circle as a guide and fill in the centre of the circle with more meringue. Pipe a second ring of rosette on top of one the circles to form a raised edge.
Bake for 1 ½ hours. changing the position of the top and bottom meringues around half way through.
Turn off the oven and leave very slightly ajar. Allow the meringues to cool in the oven.
When the meringues are completely cold, melt the chocolate pieces in a bowl over a pan of hot water. Carefully remove the meringues from the parchment and spread melted chocolate over the bottom of each meringue. Leave upside down until the chocolate has set. Alternatively you can place them chocolate side down on clean parchment.
Whip the cream until standing in soft peaks. Spoon about ⅓ into a piping bag fitted with a large star nozzle, set aside. Place the first meringue circle on a serving plate and spread half of the remaining cream over the meringue. Sprinkle about ⅔ of the raspberries over the cream.
Place the second meringue on top and gently push down slightly. Spread with a layer of cream and sprinkle about ⅔ of the blueberries.
Finally place the third meringue with the raised edge on top and gently push down. Pipe the cream in a swirly pattern on top and pile the remaining fruit into the centre. Chill until required.
Use a cake tin or a 20cm/8in dinner plate as a guide to draw the circles on parchment. A little blob of meringue in each corner can be used to stick the parchment to the baking sheet, to hold it still and make piping easier. If you do not have three shelves in your oven. Up turn a grill rack and place on the bottom of the oven so that the baking sheet is not directly sitting on the base of the oven.Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)