Both are baked egg custards. That single shared ancestor is why people mix them up. Here is the honest breakdown.
A flan, the kind we build here, is the dessert known elsewhere as creme caramel: a sweet baked custard of eggs, milk and sugar, set over a layer of caramel, turned out of its mould and served cold. No pastry. It wobbles, and the wobble is the point.
A quiche is savoury. It is a shortcrust pastry case filled with a custard of eggs and cream, plus things like bacon, cheese and vegetables. It is baked in its crust, sliced like a tart, and eaten warm as a meal rather than after one.
| SPEC | FLAN | QUICHE |
|---|---|---|
| CLASS | Dessert custard | Savoury tart |
| CUSTARD BASE | Eggs, milk or cream, sugar | Eggs, cream, seasoning |
| SWEET / SAVOURY | Sweet | Savoury |
| CRUST | None, set in a caramel-lined mould | Yes, shortcrust pastry case |
| SIGNATURE | Caramel top, inverted to serve | Fillings: lardons, cheese, veg |
| COOKING | Baked in a water bath, then chilled | Baked in the tin, served warm |
| SERVED | After dinner, cold | As the meal, warm |
| ORIGIN | Roman roots, via Spain and Latin America | Lorraine, on the French and German border |
| WOBBLE | High. Essential. | Low. Sliceable and firm. |
The trouble is that flan is an overloaded term. In British kitchens a flan can mean an open pastry or sponge case with a filling, and in France a flan patissier is a custard tart baked in pastry. Under those definitions, a quiche is fair to describe as a savoury flan.
So the two words genuinely overlap at the edges. We simply scope the word tightly: at Flanthropic, flan always refers to the wobbling caramel custard, never the crust.
If it wobbles, weeps caramel and turns up after dinner, it is a flan.
If it has a crust, bacon and turns up at lunch, it is a quiche.
Put simply: a quiche is a flan that got a job.