Preheat oven at 160°C/320°F. Line the bottom and sides of a 20x30cm (8x12 inch) baking sheet with parchment paper.
For the merengue: Whip egg whites until foamy. Add sugar, a tablespoon at a time, beating well after each addition. Beat until stiff and glossy. Stir in vinegar, cornstarch and vanilla with a wooden spoon. Pour into the prepared baking sheet and spread it evenly. Sprinkle with chopped pistachios. Bake for 30 minutes or until cooked through and the top is crispy. Let cool and turn it out up-side down onto a sheet of parchment paper dusted with powdered sugar. Carefully peel off the top paper.
For the Lemon Curd: In a saucepan combine egg yolks, sugar, lemon juice and zest. Cook over low heat whisking constantly until the mixture thickens. Add butter and whisk until creamy. Transfer to a bowl and chill.
Assembling: Mix the whipped cream with the lemon curd and spread over the reserved merengue, leaving a 1-inch border. Top with the red fruits. Roll it up using the paper to help you. Chill for at least an hour. Optional: Right before serving, cover it with whipped cream, sprinkle with pistachios, decorate with red fruits and dust with powdered sugar.