No-Bake Lemon Tart

In a food processor, blend the shortbread cookies until finely ground. Combine with granulated sugar and melted butter in a bowl. Stir until the mixture resembles wet sand.
Form the Crust:
Press the crumb mixture evenly into the bottom and sides of a tart pan, using the back of a spoon or your fingers. Refrigerate the crust while you prepare the lemon curd.
Make the Lemon Curd:
In a heatproof bowl, whisk together lemon juice, lemon zest, egg yolks, and sugar. Place the bowl over a pot of simmering water (double boiler method) and stir constantly for 10-12 minutes until the mixture thickens.
Add the Butter: