How to Make It
Preheat the oven to 225°. Line a large baking sheet with parchment paper.
In the bowl of a stand mixer fitted with the whisk, beat the egg whites with the cream of tartar and 1/2 teaspoon of salt at high speed until foamy, 2 minutes. At medium speed, gradually beat in 1 1/2 cups of the sugar, then beat at high speed until stiff peaks form, about 8 minutes. Beat in the vanilla.
Using a large spoon, dollop the meringue onto the prepared sheet and spread into a 12-inch oval. Bake the meringue for about 1 hour and 45 minutes, until crisp but still chewy on the inside. Turn the oven off and let the meringue rest in the oven for 1 hour. Transfer the baking sheet to a rack and let the meringue cool completely, about 1 hour and 30 minutes.
Light a grill or preheat a grill pan. Layer 2 large sheets of heavy-duty foil. On the foil, toss half each of the strawberries and raspberries with the lemon juice and the remaining 2 tablespoons of sugar. Fold the foil over the berries and seal the packet. Grill over high heat until juicy, about 8 minutes. Transfer to a medium bowl and let cool completely.
In a stand mixer fitted with the whisk, beat the heavy cream with the raspberry preserves until stiff peaks form. Spoon the raspberry whipped cream onto the cooled meringue. Spoon the grilled berries onto the whipped cream, then scatter the remaining fresh strawberries and raspberries on top. Serve right away.