Heat the oven to 150 ̊C/fan 130 ̊C/Gas 2. Oil 3 baking trays and line with baking parchment. Draw a circle on each roughly 23cm in diameter (I trace around a cake tin).
In a clean mixing bowl, whisk the egg whites until they begin to peak, then add the sugar a spoonful at a time, whisking all the while. When all the sugar has been added and the mixture is glossy, gently fold in the cornflour and the vinegar. Spoon the meringue on to the baking trays, spreading it out to make 3 discs. Bake for 1 hour, then switch the oven off and leave the meringues in there to harden for another hour. You want the meringue to be crisp so that it can support the weight of the cream.
You can make the meringue up to 3 days in advance and store it in an airtight container.
To make the filling, whip the cream with an electric whisk until peaks form, but take care not to over-whip it, or it will lose that silky quality.
Take the first meringue disc and spoon roughly one-third of the cream on top, then sprinkle with one-third of the berries, half the flaked almonds and 1 tbsp caster sugar. Top with the second layer of meringue and repeat. Top with the third meringue, spoon on the last one-third of the cream and decorate with berries, thyme sprigs and flowers (just make sure they’re not noxious), if you like.