A blind-baked pâte sucrée shell (Entry 21) filled with lemon curd — egg yolks, eggs, sugar, lemon juice, and butter — cooked to a set and poured into the shell while still warm. The finished tart is glossy, bright yellow, with a filling that is simultaneously sharply acidic, richly eggy, and smooth to the point of silk. Tarte au citron is among the most flavour-precise preparations in the classical patisserie repertoire: its balance between acid (lemon), sweet (sugar), and fat (butter and egg yolk) determines whether the filling tastes vibrantly sharp or overly sweet, correctly balanced or one-dimensional.
**Ingredient precision:** - Lemon: unwaxed, for both juice and zest. The zest is as important as the juice — it carries the lemon's aromatic citrus oils (limonene, citral) that the juice alone does not supply. Without zest, the tart tastes of acid but not of lemon. - Eggs: 3 whole eggs plus 4 yolks per 200ml lemon juice. The whole eggs provide the structural set; the yolks provide richness, colour, and flavour. - Sugar: 180g per 200ml lemon juice. The balance point: with less sugar, the tart is bracingly sharp; with more, it is sweet and flat. - Butter: 80g cold butter, added off heat to the hot curd and incorporated by whisking or a stick blender — the butter's fat produces the silk texture and moderates the sharpness. **The lemon curd:** 1. Combine lemon juice, zest, sugar, and eggs in a heavy saucepan. 2. Cook over medium-low heat, whisking continuously until the curd thickens — approximately 82°C. Do not boil: boiling scrambles the eggs. 3. Off heat: add the cold butter in pieces. Whisk or blend until completely incorporated. 4. Strain through a fine sieve. 5. Pour immediately into the blind-baked, warm shell. 6. Set at room temperature for 1 hour, then refrigerate. Decisive moment: The butter incorporation off heat — at the moment the cooked curd is at maximum temperature and before it begins to cool and set. The butter must be incorporated into the hot curd while it is still fluid enough to achieve full emulsification — this produces the silk. Cold curd + butter = a separated, greasy finish. Hot curd + cold butter, whisked continuously = silk. Sensory tests: **Taste — the balance test:** Taste the finished curd before pouring. It should taste simultaneously: sharply bright from the lemon juice, sweet but not cloying, richly round from the butter and egg yolk. If it tastes too sharp: add 10g more sugar. If it tastes too sweet: add 15ml more lemon juice. The balance is everything in this preparation. **Sight — the finished tart:** Deep, glossy, even yellow — the colour of a good Hollandaise. Pulled from the shell at the edge: it should hold its shape cleanly. A correctly set curd does not flow when the tart is tilted gently.
- Pass the warm curd through a fine sieve directly into the tart shell — removes the zest fibres and any coagulated egg solids in a single step - A thin torch-caramelised sugar surface on the finished, cold tart produces a crème brûlée-style crunch that gives the preparation a textural dimension beyond the smooth-only filling - A tablespoon of good olive oil added with the butter produces a slightly fruitier, more complex finish — the olive oil's fruity esters complement the lemon in a way that butter alone does not
— **Scrambled eggs in the curd:** The curd was heated too quickly or reached boiling temperature. Cook over medium-low, stirring constantly, and remove from heat well before 100°C. — **Greasy, separated texture:** Butter added to a curd that had cooled too far before incorporation. The emulsification requires the curd to be above 50°C when the butter is added.
Jacques Pépin's Complete Techniques