Make the gluten-free pastry

• Mix the gluten-free flour, salt and caster sugar in a bowl.
• Rub in the cold cubed butter until the mixture resembles breadcrumbs.
• Add the beaten egg and ice-cold water and bring together into a dough.

Chill the dough

• Shape the dough into a disc, wrap it and chill until firm.

Blind bake the crust

• Roll the dough out and line the pie dish, then prick the base.
• Chill again briefly, then bake at 190 °C until pale golden.
• Remove the baking beans and bake a few more minutes until the base is dry.

Cook the lemon filling

• Whisk the cornflour, caster sugar and water in a saucepan until smooth.
• Add the lemon zest and juice and cook over medium heat, stirring, until thick and glossy.
• Take off the heat and whisk in the egg yolks and butter until smooth.

Fill the pie

• Pour the warm lemon filling into the baked crust and smooth the top.
• Let it set while you make the meringue.

Whip the meringue

• Whisk the egg whites with the cream of tartar until soft peaks form.
• Add the caster sugar gradually and whisk until stiff, glossy peaks form.

Top and bake

• Spoon the meringue over the filling, spreading it to the edges and making peaks.
• Bake at 180 °C until the meringue is golden.

Cool and serve

• Cool the pie completely so the filling sets before slicing.