Combine 200 g of unsalted butter and 100 g of superfine sugar in a food processor, pulsing until creamy. Add 1 whole egg, 1 egg yolk, and 1 teaspoon of vanilla extract, blending until well incorporated. Gradually mix in 350 g of cake flour and ½ teaspoon of salt until a dough forms.

Wrap the dough in plastic wrap and refrigerate for at least 1 hour to firm up.

Preheat your oven to 140°C (290°F). Roll out the chilled dough and cut into small discs. Press these discs into mini tart tins. To blind bake, line the pastry with parchment paper and fill with rice or pie weights, then bake for 15 minutes.

While the pastry cools, whisk together 2 tins of condensed milk, 3 egg yolks, 80 ml of lemon juice, and 1 tablespoon of lemon zest in a bowl. Fill the baked pastry shells with this mixture and return to the oven at 160°C (320°F) for 15 minutes.

Remove the tarts from the oven and allow to cool in the tins for about 15 minutes, then transfer to a wire rack.

In a heatproof bowl, combine 4 egg whites and 200 g of superfine sugar over a double boiler. Whisk continuously until the sugar has dissolved and the mixture is warm. Beat until stiff peaks form.

Once the tarts are cool, swirl the meringue onto each tart and torch lightly until golden brown.