For the meringues:
1 Preheat the oven to 130 degrees, or 110 degrees if using a fan oven. Line a baking tray with a sheet of parchment paper.
2 Whisk the egg whites and salt together using a stand mixer or electric whisk until frothy. Add the sugar gradually, a tablespoon at a time, and continue to whisk to stiff peak, about five minutes.
3 Add the vinegar and sift in the cornflour, and gently fold in until well combined.
4 Put the meringue in a piping bag fitted with a large star nozzle, or alternatively, use a Ziploc bag.
5 Pipe different sized small stars of meringue on the prepared baking sheet and bake the meringues in the preheated oven for 10 minutes, then reduce the heat to 110 degrees or 90 degrees fan and continue to bake for another 30 minutes. Turn off the oven and leave to cool in the oven for 10 minutes.
For the sponge:
1 Preheat the oven to 180 degrees, or 160 degrees fan. Grease and line a 30x20cm rectangle baking tin.
2 Cream the butter and sugar together until pale. Add the eggs one by one, beating in each one until fully combined.
3 Sift in the flour and add the vanilla, followed by the milk and mix until just combined.
4 Pour the batter into the tin and arrange the strawberries on top. Bake in the preheated oven for 45 minutes, until a skewer inserted into the centre comes out clean.
5 Remove from the oven and leave to cool slightly before turning out onto a wire rack to cool completely.
For the cream:
1 Whisk the cream, icing sugar and vanilla together to soft peak. Fold in the elderflower cordial (if using) followed by the yoghurt.
1 Pile the cream on top of the cooled sponge and arrange the halved strawberries on top.
2 Place a few meringues in and around the strawberries, crushing a few to make a coarse powder.
3 Garnish with edible flowers (if using) and cut into squares to serve.