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• Boil the filling for a full minute. Cornstarch does not reach full thickening power until it boils, and lemon juice's acid breaks starch chains down over time. Add the juice at the very end, off the heat, for the same reason.
• Put the meringue onto a hot filling. This is the fix for a weeping layer. Meringue spread on cold curd cooks only on top; the underside stays raw and releases liquid. Hot filling cooks it from below.
• Seal the meringue to the crust all the way round. Meringue that does not touch the pastry rim shrinks inward as it cools.
• Italian or Swiss meringue is far more stable than French for this. Swiss — whites and sugar heated to 70 °C over a bain-marie, then whipped — is the easiest reliable option.
• Cool slowly, at room temperature, and never in the fridge uncovered. Refrigeration is what makes meringue bead.

One 23 cm pie. Serves 10.

• 1 blind-baked shell — all-butter pie crust

Filling:

• 300 g granulated sugar
• 60 g cornstarch
• 4 g fine salt
• 400 ml water
• 5 egg yolks
• 60 g unsalted butter
• 180 ml lemon juice, about 4 lemons
• zest of 3 lemons

Swiss meringue:

• 5 egg whites
• 250 g granulated sugar
• 2 g cream of tartar
• pinch of salt

Blind bake the shell and keep it warm.

Whisk the sugar, cornstarch and salt in a saucepan, then whisk in the water. Cook over medium heat, whisking, until it thickens and boils. Boil one minute.

Temper the yolks: whisk a ladle of the hot mixture into them, then pour that back into the pan. Cook two minutes more, whisking hard.

Off the heat, whisk in the butter, then the lemon juice and zest. Pour into the shell and keep it hot.

For the meringue, whisk the whites, sugar, cream of tartar and salt in a bowl over simmering water until it reaches 70 °C and the sugar is fully dissolved between your fingers. Whip at high speed until stiff, glossy and cool, about six minutes.

Spread the meringue onto the hot filling immediately, sealing it to the pastry edge all the way round, and lift it into peaks.

Bake 175 °C / 350 °F for 12–15 minutes, until the peaks are gold, or torch it.

Cool at room temperature three hours. Do not refrigerate before it is completely cold.

• Cut with a wet knife, dipped in hot water and wiped between slices.
• Lime, orange, passion fruit and grapefruit all work in the same filling with the sugar adjusted.
• Eat it the day it is made. Meringue on a wet filling is on a clock; by day two it has begun to dissolve.

Method and theory: Pie and tart recipes · pies and tarts · lemon · eggs

Nearby: key lime pie · lemon tart · banana cream pie