A traditional key lime pie has a whipped cream topping, but this Italian meringue topping makes the pie lighter on the palate– try this technique on lemon meringue pie, too!
Unlike commercially made key lime pies, the colour of the lime custard is not green, but more of a yellow colour, or even light orange if using calamansi limes (a lovely aromatic lime from the Philippines).
Preheat the oven to 350 °F (180 °C).
Stir the graham crumbs, coconut and melted butter together until crumbly and press this into an ungreased 9-inch (23 cm) pie plate. Bake the crust for 10 minutes, then cool before filling.
For the filling, reduce the oven temperature to 300 °F (150 °C). Whisk the condensed milk with the lime juice, zest and vanilla and then whisk in the egg yolks (save the whites for the meringue). Pour this into the cooled crust and bake for 30 minutes, until the filling no longer jiggles when the pan is moved. Cool the pie to room temperature. Once cooled, the pie can be chilled and topped with meringue later.
Increase the oven temperature to 400 °F (200 °C). Whip the whites and cream of tartar with electric beaters or in a stand mixer fitted with the whip attachment until they are just past foamy (frothy but not holding a soft peak). Bring the sugar with 3 Tbsp (45 mL) of water up to a boil on high heat without stirring. Continue to boil the sugar until it measures 240 °F (115 °C) on a candy thermometer. Carefully pour the sugar down the side of the bowl while beating on high speed and continue whipping until the meringue is almost at room temperature, about 5 minutes.
Place the meringue in a large piping bag fitted with a large star tip. Pipe a pattern of your wish (spikes upward or spiral around) on top of the cooled filling (alternatively, you can dollop and spread the meringue over the filling). Bake this for 4-5 minutes, until the meringue browns as desired (keep an eye on it, it can brown quickly!) Alternatively, the meringue can be browned using a butane torch (since the meringue is fully cooked, the torching is for effect). Cool the pie to room temperature and then chill completely (2-3 hours) before serving.