Step 1

For the pastry, put the flour, butter, icing sugar, egg yolk and 1 tbsp cold water into a food processor. Process until the mix starts to bind. Tip the pastry onto a lightly floured surface, gather together until smooth, then roll out and line a 23 x 2.5cm deep loose- bottom flan tin. Trim and neaten the edges. Prick the base with a fork, line with foil, shiny side down, and chill for 1 hour.

Step 2

Heat oven to 200°C. Blind bake the pastry case for 15 minutes, then remove the foil and bake a further 5-8 minutes until the pastry is pale golden and cooked. Set aside. Lower the oven to 180°C.

Step 3

While the pastry bakes, prepare the filling: mix the cornflour, sugar and lemon zest in a medium saucepan. Strain and stir in the lemon juice gradually. Make enough orange juice up to 200ml with water and strain into the pan. Cook over a medium heat, stirring constantly, until thickened and smooth. Once the mixture bubbles, remove from the heat and beat in the butter until melted. Beat the egg yolks and whole egg together, stir into the pan and return to a medium heat. Keep stirring vigorously for a few minutes, until the mixture thickens and plops from the spoon. Take off the heat and set aside while you make the meringue.

Step 4

Put the egg whites in a large bowl. Whisk to soft peaks, then add half the castor sugar a spoonful at a time, whisking between each addition without overbeating. Whisk in the cornflour, then add the rest of the sugar as before until smooth and thick. Quickly reheat the filling and pour it into the pastry case. Immediately put spoonfuls of meringue around the edge of the filling, then spread so it just touches the pastry. Pile the rest into the centre, spreading so it touches the surface of the hot filling, then give it all a swirl. Return to the oven for 18-20 minutes until the meringue is crisp and lightly coloured. Let the pie sit in the tin for 30 minutes, then remove and chill for at least another 30 minutes before slicing and serving.