Preheat the oven to 325 degrees.
In the bowl of an electric stand mixer fitted with the whisk attachment, combine the egg yolks, sweetened condensed milk, lime juice, sugar, and zest. Beat on medium speed for 1 minute or until well blended. Spoon into crust. Set aside.
If you're using the same mixing bowl and whisk for the meringue, make sure it is clean and completely dry.
In the bowl of an electric stand mixer fitted with the whisk attachment, beat the egg whites on high speed until soft peaks form. With the mixer still on high speed, slowly add the sugar and cream of tartar and continue beating until stiff peaks form.
Spread the meringue over the filling, completely covering the filling to the edge of the pastry. Bake for 30 minutes or until the meringue is golden brown. Chill for 2 hours or overnight before serving.
Tips for a perfect meringue