Draw three circles measuring 24 cm in diameter on greaseproof paper and place on baking sheets. Grease inside the circles and sprinkle them with flour. Set the oven temperature to just under 125°C.
Whisk the egg whites and Siúcra/McKinney's Granulated Sugar in a mixing bowl over a water bath until the meringue is thick and firm. Pipe or spread the meringue inside the circles.
Put all the baking sheets in the oven at once, swapping them round occasionally. Bake for about two hours. Remove the paper from the meringue disks. Leave to cool on a wire rack.
Whip the cream and Siúcra/McKinney's Granulated Sugar until soft peaks form. Top and tail the berries and fold them into the cream. Spread two of the discs with the cream mixture and sandwich the three discs together. Decorate the top disc with fresh berries.