Are The Eggs In Bitter Orange Tart Fully Cooked?

Our answer

Nigella's Bitter Orange Tart has a ginger biscuit (snap) crust that is filled with a Seville orange curd. Seville oranges have a tart flavour, hence the "bitter orange" description, but out of the short Seville orange season it is possible to use a mixture of regular oranges and limes.

The curd is made with a mixture of citrus juice, sugar, butter and egg yolks and this mixture is cooked until thick. In effect it is a type of custard. Eggs generally start to thicken (coagulate) at around 70°C but with curds the acid and sugar in the mixture raises this threshold slightly and most curds will thicken between 75°C and 80°C. Salmonella is usually killed at around 71°C, so curds, and custards, are usually considered to have very low risk of contamination from salmonella. If you are concerned then you can use an instant-read thermometer to check the temperature of the curd as it cooks.