Begin by rolling out your pie dough and fitting it into a pie pan. Chill the crust in the fridge for 30 minutes. Preheat your oven to 375°F (190°C). Once chilled, line the crust with parchment paper and fill with weights. Bake for 30 minutes, then remove the weights and parchment. Reduce the oven temperature to 350°F (175°C) and continue baking for another 15 minutes until the crust is lightly golden.

Zest and juice your fresh lemons, then combine the zest and sugar in a medium saucepan over medium heat. Stir and heat until the sugar dissolves. Next, whisk in the eggs and fine sea salt. Cook the mixture while continuously stirring until it thickens and reaches 160°F (70°C). Remove from heat and strain into a bowl, mixing in the melted butter and tapioca starch or cornstarch until everything is well incorporated.

Pour the velvety lemon filling into the pre-baked pie crust. Smooth the top with a spatula and bake in the oven at 350°F (175°C) for about 15-20 minutes. You'll know it’s ready when the filling is just set in the center and has a slight jiggle, which will firm up as it cools. Remove from the oven and let it cool at room temperature.

Set up a double boiler by simmering water in a pot. Place a heatproof bowl over the pot and whisk together egg whites and granulated sugar until the sugar dissolves. Monitor closely, whisking for about 5 minutes. Then transfer the mixture to a stand mixer and whip on high speed until you achieve stiff peaks, adding cream of tartar and vanilla towards the end. The meringue should be glossy and hold its shape well.

Spread the fluffy Swiss meringue generously over the cooled lemon filling, making decorative swirls for an elegant touch. Use a kitchen torch to gently toast the meringue until it turns a delicate golden brown, or place the pie under the broiler for about 1 minute watching closely to avoid burning. Once done, allow the meringue topping to cool slightly before slicing into your Lemon Meringue Pie.