Marco Pierre White’s tarte au citron from Harveys — a sharp, dense lemon custard, no starch, set only by eggs and baked in a low oven until it barely holds. Nine eggs, a lot of sugar, the juice of five lemons, and cream, poured cold into a hot tart shell and baked at 250°F. Finished, if you like, with a blowtorched sugar glass.

Ingredients

   
1 batch tart shell — blind-baked (see step 3)
  Lemon filling
9 eggs (~450g)
400g caster sugar
2 lemons, zested
250g lemon juice (about 5 lemons)
250g double cream (or heavy cream)
  Finish
50g confectioners’ sugar

Steps

  1. Line a deep (≥3.5cm) 8-inch loose-bottom tin or tall ring with a batch of tart shell dough, pressing the walls tall, and chill it while you make the filling.

  2. Filling: whisk the eggs, caster sugar, and lemon zest until smooth — mix to dissolve, don’t whip air in. Stir in the lemon juice, then fold in the cream. Skim the froth off the top, then let it rest 15–30 minutes and skim again; a clear, bubble-free mix sets to a smooth, glassy surface.

  3. Blind-bake the shell: at 350°F, 15 minutes with pie weights, then lift out the weights and bake 5–8 minutes more, until evenly golden and dry. For insurance against the acidic custard, brush the hot base with a little egg white and return it for 2 minutes to seal.

  4. Drop the oven to 250°F. With the shell still hot, pour the cold filling in to just below the rim. Cold-into-hot sets the base on contact and seals it.

  5. Bake at 250°F for 30–45 minutes, until the filling is just set with only a faint wobble at the very center — it should quiver as one piece, not ripple like liquid. It firms further as it cools.

  6. Cool completely, at least 1 hour — it is too runny to cut warm. For the classic finish, dust the top evenly with the confectioners’ sugar and caramelize it under a very hot grill or with a blowtorch to a thin glass. Serve at room temperature or lightly chilled.

Analysis

Total filling: 1350g (tart shell and the 50g sugar glaze excluded)

Component Amount %
Liquid (egg water, lemon juice, cream water) 715g 53.0%
Sugar 411g 30.4%
Fat (cream, egg) 165g 12.2%
Egg/protein 59g 4.4%
Structure solids — —

This is a pure egg-set custard — no starch at all — which is the whole reason for the 250°F oven. Flan pâtissier carries ~4.8% cornstarch, and starch granules shield the egg proteins so that custard can be boiled on the stove and baked hot; strip the starch out and the only thing setting the tart is 4.4% egg protein, which curdles into scrambled egg above ~185°F. A low oven keeps the custard under that point while the proteins coagulate slowly and evenly. Two things push the same way: the 30.4% sugar (against flan’s 13%) raises the temperature at which the eggs set and slows it, keeping the custard silky; and the lemon juice’s acid helps the proteins bond, which is why a starchless citrus custard sets firmer than its numbers suggest. It sits between the pure egg-set purin and the yolk-and-cream crème brûlée — more egg and more sugar than either, no starch like the flan.

Notes

  • The low oven is the technique, not a suggestion. 250°F is what keeps a starchless egg custard from curdling (see the Analysis). A hotter oven is faster but gives you a grainy, weeping, or cracked set. If yours browns or souffles up, the oven is too hot — it should stay pale and flat.
  • Pour cold into hot. The cold filling meeting the hot shell sets the base immediately, which both seals the pastry against the wet custard and keeps the crust crisp. It’s Marco’s shortcut in place of a separate egg-wash seal — though the egg-white brush in step 3 is cheap extra insurance against a soggy or leaking base.
  • Skim the foam and let it rest. Bubbles whisked into the filling rise and bake into a pocked, cloudy surface. Skimming twice and resting gives the glassy top the blowtorch then turns to caramel.
  • Double cream vs. heavy cream. British double cream is ~48% fat and sets the custard richer and firmer; American heavy cream (~35%) works and bakes a touch softer and looser. Neither changes the method.
  • The wobble is the doneness cue. Pull it while the center still jiggles as a single mass; baked until firm all through, it cracks and dries. It’s a soft, sliceable custard, not a solid curd — the clean cut comes after the full cool.
  • Capacity — this is a lot of filling. The full batch is ~1350g, sized for a deep 8-inch tin (Marco’s is 3.75cm deep) or a generous 9-inch. In a shallow shell it will overflow: line the walls tall, or bake the excess in ramekins in the same 250°F oven (~25 minutes). Don’t fill past ~3mm below the rim.
  • The glaze is optional. Uncaramelized, it’s a plain, clean lemon tart; blowtorched, it gets a brûlée-like snap. Do it just before serving — the sugar glass softens within an hour or two in the fridge.
  • Lemons. Five lemons give about 250g of juice; zest only 2 so it doesn’t turn bitter or bready. Zest before juicing.
  • Storage. Keeps 2–3 days refrigerated. Cut with a hot, dry knife. If you’re glazing, glaze slice-by-slice or the whole top goes tacky in the fridge.
  • The shell is its own recipe: tart shell (Dominique Ansel’s vanilla sablé) — a sweet, sandy sablé rather than the flaky pâte brisée, with its rolling, lining, and blind-baking detail there.