In a food processor, blend the unsalted butter and superfine sugar until the mixture is smooth and creamy, about 2 minutes. Add in the whole egg, egg yolk, and vanilla extract, pulsing until well combined. Gradually incorporate the sifted cake flour and salt until a dough forms. Chill the dough in the refrigerator for about an hour, then roll it out to about 1/8-inch thickness to fit into your mini tart tins.

Preheat your oven to 140°C (290°F). Carefully press the rolled-out pastry into the prepared mini tart tins, ensuring an even layer. Line each pastry shell with parchment paper and fill with rice or beans to prevent puffing. Bake for approximately 15 minutes or until lightly golden, then remove from oven and allow to cool completely.

Whisk together the condensed milk, egg yolks, lemon juice, and zest in a mixing bowl until smooth. Carefully fill each pre-baked pastry shell with the lemon mixture. Bake in the oven at 160°C (320°F) for about 15 minutes, until the filling is set but still slightly jiggly in the center. Allow tarts to cool before adding meringue.

Whisk the egg whites and superfine sugar over a double boiler. Gently heat while whisking until the sugar dissolves and mixture is warm. Transfer to a stand mixer and beat on high speed until glossy, stiff peaks form, about 5 minutes.

Pipe the meringue generously over each lemon curd filling. Use a kitchen torch to brown the meringue until golden and slightly toasted.