Step 1: Make the pastry

In a mixing bowl, rub the butter into the flour until the mixture resembles breadcrumbs. Stir in the icing sugar. Add the egg yolk and cold water, mixing until the dough comes together. Wrap in cling film and chill for 30 minutes.

Step 2: Roll out and blind bake

Preheat your oven to 200°C (400°F). Roll out the pastry on a floured surface and line the tart tin. Prick the base with a fork, line it with baking paper, and fill it with baking beans or rice. Bake for 10 minutes, then remove the paper and beans and bake for another 5 minutes until golden. Reduce the oven temperature to 180°C (350°F).

Step 3: Prepare the lemon filling

In a saucepan, mix the cornflour and caster sugar. Gradually whisk in the water, lemon juice, and zest. Cook over medium heat, stirring constantly, until the mixture thickens. Remove from heat and whisk in the butter and egg yolks until smooth.

Step 4: Make the meringue

In a clean mixing bowl, whisk the egg whites until they form stiff peaks. Gradually add the caster sugar, one spoonful at a time, whisking until the meringue is glossy and holds firm peaks.

Step 5: Assemble the pie

Pour the lemon filling into the baked pastry shell. Spread the meringue evenly over the filling, ensuring it touches the edges of the pastry to seal. Swirl the meringue with a spatula for decorative peaks.

Step 6: Bake

Bake the pie in the preheated oven for 15-20 minutes, or until the meringue is golden and firm. Allow to cool slightly before serving.