Preheat the oven to 150°C/300°F/gas 2. Put your egg whites into a clean bowl and whisk them at a medium speed until they start to form nice firm peaks.
With your mixer still running, gradually add the sugar and a pinch of salt. Turn the mixer up to the highest setting and whisk for 7-8 minutes more until the meringue is white, glossy and smooth. If it feels grainy, whisk for a little bit longer, being careful not to let the meringue collapse.
Line two baking trays with baking paper. Divide the meringue mixture evenly between them and shape each blob into a circle about 20cm in diameter. Put both trays into the oven and bake for 1 hour until the meringues look slightly golden and are fluffy in the middle.
Halve or quarter the large strawberries and leave the smaller ones whole. Mix them with the raspberries. Whip the cream with the sugar until it forms soft peaks, then stir in the yoghurt and fold in the vanilla seeds. Spoon half the cream mixture on top of one of the meringue halves and smooth it out. Sprinkle half of your berries evenly around the cream mixture. Place the other meringue on top and press down gently to stick them together. Spread the remaining cream mixture over the top layer and sprinkle the remaining berries on top. Scatter over a few small mint leaves and enjoy!