Preheat oven to 200C. To make pastry, put butter, icing sugar and vanilla in a food processor and pulse until a coarse crumb forms. Add egg and pulse 3 times. Add flour and baking powder and pulse until dough just comes together. Roll out dough and line a deep 23cm pie dish, or a deep 23cm fluted loose bottom quiche tin. Freeze for 15 minutes or until firm. Remove from freezer, prick dough with a fork and bake for 10 minutes until just golden.
To make the filling, put egg yolks, sugar and cornflour, and lemon zest and juice in a double broiler and cook, stirring constantly, for 10 minutes or until the mixture is thick. Pour into pastry shell.
To make the meringue, whisk egg whites and cream of tartar, using an electric mixer on high until stiff peaks form. Continue whisking and add sugar, 1 tablespoon at a time, until meringue is thick and glossy. Spoon meringue on top of filling. Reduce oven to 150C and bake pie for 45 minutes, until the meringue is lightly browned and firm. All to cool for 30 minutes before serving.