Preheat the oven to 325 degrees F.
For the crust: Place the graham cracker crumbs and sugar in a bowl and stir to combine. Add the butter and stir until crumbs are all moistened.
Pour the graham cracker mixture into a 9 inch non stick tart pan or pie pan. Firmly press the mixture into the bottom and sides of the pan.
Bake the crust for 10-12 minutes or until lightly browned.
For the filling: While the crust is baking prepare the filling. Whisk the eggs and sugar together in a bowl until smooth.
Whisk in the lemon juice until thoroughly incorporated.
Whisk in the cream and then strain the filling through a sieve into a large measuring cup and stir in the zest. The filling will be quite liquid at this point.
Without removing the crust from the oven, pour the filling into the crust. You may have leftover filling if you're using a tart pan; just pour the leftover into a greased ovenproof dish and bake it along with the tart for a snack for later on.
Bake the tart for 35-40 minutes until the center is just set. Cool the tart on a rack and then refrigerate for at least an hour.
For the meringue: Place the egg whites and cream of tartar into a stand mixer fitted with a whisk attachment.
Place the brown sugar into a medium heavy saucepan and add just enough water to cover.
Put your candy thermometer on the pan and turn the heat to high.
When the sugar reaches 240 degrees, start whipping the egg whites by turning your mixer to high speed; you want the egg whites to be foamy and starting to thicken before you add the sugar syrup.
When the sugar reaches 245 degrees, remove the thermometer from the pan and turn the mixer speed down to medium.
Pour the sugar into the egg whites in a thin, steady stream avoiding the moving whisk. When all the sugar has been added, continue whipping until the meringue reaches the firm peak stage.
Quickly spread the meringue over the tart with a large spoon or offset spatula. Use your torch to brown the outside of the meringue. Store the tart in the fridge until ready to serve.