Preheat the oven to 175°F (80°C). In a mixer bowl with a whisk attachment, whisk the egg whites until a white foam begins to form. Gradually add the sugar and continue whipping on high speed for 7 to 10 minutes until a smooth, shiny, and stiff meringue forms. Sift the powdered sugar into the meringue and mix until smooth. Line a baking tray with parchment paper and pipe the meringue. Bake for two to three hours. Remove and let cool at room temperature, preferably overnight.

Place the frozen strawberries, sugar, and lemon juice in a small saucepan. Bring to a boil and reduce slightly. You can blend the sauce or serve it with fruit pieces. Store in a container until serving.

In a bowl, combine the heavy cream and mascarpone. Add the powdered sugar and vanilla, and whip until stiff peaks form. Transfer the whipped cream to a piping bag with a round tip.

Place the baked meringue on a serving plate. Pipe the mascarpone whipped cream on top, pour the prepared strawberry sauce in the center, arrange fresh berries on top, and serve immediately.