Why Is The Filling For My Bitter Orange Tart Too Runny?

Our answer

Nigella's Bitter Orange Tart (from SIMPLY NIGELLA) has a ginger biscuit or ginger snap crust that is filled with a Seville orange curd. The curd is cooked in a saucepan and then left to cool and thicken, before it is transferred to the tart base.

If a curd is too thin then it usually means that it has not cooked for long enough. With a curd the heat needs to remain fairly low and sometimes you need to be a little patient. Don't whisk too vigorously while the curd is cooking, just stir gently and constantly. The curd is done when it coats the back of a spoon and if you draw your finger through the curd on the spoon it leaves a channel and does not flow back. The eggs are the main thickener in a curd and they need to reach 76-77C/170F before they start to thicken. If you have an instant-read thermometer then you could use this to help to judge when the curd should start thickening. However, be careful not to cook the mixture too quickly or for too long, as the mixture can get small flecks of overcooked egg in it (if this happens pass the mixture through a fine sieve or strainer). You should also make sure that the eggs are large (US extra large) as the ratio of eggs to liquid is important. It also helps if the eggs are as fresh as possible, as older eggs may not thicken as well as fresh ones.