Lemon Meringue Pie — sharp lemon filling under a golden meringue

i. Origin & history

Lemon tarts and lemon creams were made in Europe long before the pie as we know it. English cooks of the seventeenth and eighteenth centuries baked lemon puddings and 'lemon cheesecakes' of lemon, sugar, eggs and butter in pastry — essentially lemon curd tarts. Meringue, whipped egg white and sugar, appears in French and English cookbooks from the late seventeenth century, and by the eighteenth century it was being used to top puddings.

The combination of lemon filling and a meringue crown developed during the nineteenth century, when cornflour (cornstarch) became cheap and available and made a stable, sliceable lemon filling easy. Recipes recognisable as lemon meringue pie appear in both British and American cookbooks from the mid- to late 1800s. In the United States, the Philadelphia cooking teacher Elizabeth Coane Goodfellow is often credited with an early version in the first half of the century, though, as with most classic desserts, the claim is difficult to verify and the dish probably emerged in many kitchens at once.

By the twentieth century it had become a fixture of British teashops, bakeries and Sunday puddings, and of American diners and Thanksgiving tables. It remains one of the most popular pies in both countries, and in Britain it is as likely to be sold by the slice in a café as served at home.

Lemon meringue pie is closely related to the French tarte au citron meringuée, which uses a richer, butter-heavy lemon cream, and to key lime pie in the United States, which uses condensed milk. It also shares DNA with the old British queen of puddings, another dessert crowned with meringue.

ii. Why the filling sets — and why meringue weeps

The lemon filling is thickened with cornflour and egg yolks. Cornflour starch only reaches full thickening power once the mixture comes to a proper boil and is held there for a minute or so. Egg yolks contain an enzyme, amylase, that can break down starch; if the filling is not cooked enough to destroy the enzyme, the pie may set and then mysteriously turn runny overnight. Boiling the filling for a minute after adding the yolks avoids this.

The lemon juice is added at the end, off the heat. Acid interferes with starch thickening if boiled with it for long, so adding the juice after the starch has set keeps the filling firm while preserving its fresh, sharp flavour.

Meringue problems are the other common frustration. Weeping — a layer of syrupy liquid between filling and meringue — happens when the underside of the meringue does not cook, so spreading the meringue onto a hot filling helps cook it from below. Beading, droplets of syrup on top, happens when the meringue is overcooked or the sugar has not dissolved. Adding the sugar gradually and baking at a moderate temperature solves both. A spoonful of cornflour in the meringue stabilises it further.

Finally, the meringue must be sealed to the pastry all round the edge. If it is not anchored, it shrinks back as it cools and slides off when the pie is cut.

iii. Ingredients

Makes 10 servings · scroll the side panel to adjust

• 200 g plain flour (pastry)
• 100 g cold unsalted butter, diced (pastry)
• 30 g icing sugar (pastry)
• 1 egg yolk (pastry)
• 2 tbsp cold water (pastry)
• 4 unwaxed lemons, zest and juice (about 175 ml juice)
• 50 g cornflour
• 300 ml water (filling)
• 175 g caster sugar (filling)
• 4 large egg yolks
• 50 g unsalted butter (filling)
• 4 large egg whites
• 200 g caster sugar (meringue)
• 1 tsp cornflour (meringue)
• ¼ tsp cream of tartar or a few drops of lemon juice

Use fresh lemons, unwaxed for the zest; bottled juice gives a flat filling. Cornflour is essential to a sliceable filling (in the US, cornstarch). The extra yolk in the pastry gives a richer, shorter crust. Caster sugar dissolves quickly in the meringue. Cream of tartar stabilises the whites; a few drops of lemon juice do the same. Shop-bought sweet shortcrust is a time-saver, but blind-bake it well.

iv. Method

1. Make the pastry: rub the butter into the flour and icing sugar until it resembles breadcrumbs. Add the yolk and water and bring together into a dough. Flatten, wrap and chill for 30 minutes.
2. Heat the oven to 190 °C (170 °C fan, 375 °F). Roll the pastry 3 mm thick and line a 23 cm loose-bottomed tart tin, leaving the edges overhanging. Chill for 15 minutes, then line with baking paper and baking beans and bake for 15 minutes. Remove the paper and beans and bake for 8–10 minutes more until golden and dry. Trim the edge. Lower the oven to 170 °C (150 °C fan, 340 °F).
3. Make the filling: in a pan, mix the cornflour, sugar and lemon zest, then gradually whisk in the water until smooth. Bring to the boil, stirring constantly, and cook for 1–2 minutes until thick and glossy.
4. Off the heat, whisk in the egg yolks one at a time, then return to the heat and bring back to a gentle boil, stirring, for 1 minute. Remove from the heat and beat in the butter and lemon juice. Pour into the pastry case.
5. Make the meringue while the filling is still hot: whisk the egg whites and cream of tartar to soft peaks. Add the sugar a tablespoon at a time, whisking well after each, then whisk in the cornflour. Keep whisking until thick, glossy and holding stiff peaks.
6. Spoon the meringue around the edge of the filling first, sealing it to the pastry, then fill in the centre. Swirl into peaks with the back of a spoon.
7. Bake for 18–20 minutes, until the meringue is crisp and golden at the tips.
8. Cool in the tin for 1 hour, then at room temperature for at least 1 hour more before slicing with a wet knife.

v. Tips & common mistakes

• Boil the filling after adding the yolks. This destroys the starch-digesting enzyme in the yolks and stops the filling turning runny.
• Add the lemon juice last. Boiling acid with cornflour weakens the set.
• Spread meringue on hot filling. The heat cooks the base of the meringue and prevents a weeping layer.
• Seal the meringue to the pastry. Anchoring it stops it shrinking and sliding.
• Blind-bake the pastry fully. An underbaked case turns soggy under the wet filling.
• Cool at room temperature, not in the fridge. Rapid chilling makes the meringue weep and the pastry soft.

vi. Variations

Lime meringue pie swaps lemons for limes; orange or blood orange versions need extra lemon for acidity. Italian meringue, made with hot sugar syrup, is more stable and can be torched instead of baked. Individual tartlets are popular in bakeries, and a digestive biscuit base makes a quick no-pastry version.

For other lemon desserts see lemon posset; for other meringue-topped puddings, queen of puddings and baked Alaska. Citrus tarts from elsewhere include the tangerine tart and lime coconut pie.

vii. Serving & storage

Serve lemon meringue pie at room temperature, on the day it is made, in generous slices. It needs no accompaniment, though a little pouring cream or crème fraîche is welcome. It is equally at home at afternoon tea or as a dinner-party dessert.

The pie is best within 12 hours. Leftovers can be kept loosely covered in the fridge for up to 2 days, though the meringue will soften and may weep and the pastry will lose its crispness. The pastry case can be blind-baked a day ahead and kept airtight. Lemon meringue pie does not freeze well.

ix. More from British & Irish

• Lemon Posset — lemon-set cream
• Queen of Puddings — custard, jam and meringue
• Bakewell Tart — almond and jam tart
• Treacle Tart — golden syrup tart
• Tangerine Tart — citrus custard tart
• Baked Alaska — meringue over ice cream