Add the graham cracker crumbs to a bowl along with the melted butter. Stir well to combine.
Press the crumb mixture into the bottom of an 8-inch tart pan and up the sides of the pan. Set aside.
Pour the sweetened condensed milk into a bowl and add the juice and zest of the 3 lemons.
Slowly pour in the heavy whipping cream, mixing with a hand mixer (or use your stand mixer fitted with the whisk attachment) while you continue to pour the whipping cream in a steady stream.
Continue mixing on medium-high speed for 2-3 more minutes until the filling becomes slightly thicker and glossy.
Pour the filling into the prepared crust and refrigerate for about 6 hours or overnight.
Slice and serve, topping each slice with a dollop of whipped cream and some lemon zest (if desired).
Video
Notes
This tart can be prepared up to one day in advance of serving and stored in the fridge in an airtight container.
Storage Instructions
This tart can be made 1-2 days in advance and stored, covered, in the fridge until ready to serve.
Freezing instructions
It can also be frozen for up to 2 weeks and defrosted in the fridge before serving. For BEST results, make only one day ahead and chill in the fridge to set.