Special equipment: a kitchen blowtorch, optional
For the crust and lemon curd filling: Bake the crust according to the package instructions. Let cool.
Add 1/4 cup water to a bowl and sprinkle with the gelatin. Let the gelatin bloom while you prepare the filling.
In a pot, bring the lemon zest and juice and half of the sugar to a boil. In a separate bowl, vigorously whisk the eggs with the remaining sugar until completely incorporated.
Bring the pot off the heat and let cool slightly. Slowly add the egg and sugar mixture to the pot, whisking continually. Using a candy thermometer, heat the mixture to 185 degrees F, whisking vigorously. Add the bloomed gelatin and butter. Mix thoroughly using an immersion blender. Strain, then pour into the pie shell. Refrigerate until completely set, about 1 hour.
For the meringue: Mix the sugar and 1/2 cup water in a pot and heat to 248 degrees F.
In a stand mixer with the whisk attachment, combine the egg whites and cream of tartar. Whisk on medium speed until soft peaks form. Switch the speed to high, slowly add the sugar and water mixture in a thin steam and whisk until fully incorporated and stiff peaks form.
Spread the meringue generously on the pie and style using a palette knife (offset spatula) as desired. With a kitchen blowtorch, gently go over the meringue until a toasted color is achieved. Or place under the boiler until browned, 2 to 3 minutes.
Propane gas torches are highly flammable and should be kept away from heat, open flame and prolonged exposure to sunlight. They should be used only in well-ventilated areas. Follow torch manufacturer's instructions for use.