The Bitter Orange Tart looked gorgeous in the Simply Nigella book and the recipe seemed straightforward so I tried it for a dinner party. Made the base a full 30 hours before with ginger nut biscuits, but even with an additional 25g butter melted in, using a slightly smaller tart tin and fridging for 29 hours it wasn't bonded. I had to pour in melted dark chocolate and briefly freeze the base before pouring in the curd and could not risk serving in front of guests as I normally would as it was crumbling as I cut it. Any suggestions as to how I could correct this problem as the taste combination is great.
Nigella's Bitter Orange Tart (from SIMPLY NIGELLA) has a crumb base made from crushed ginger nut biscuits (ginger snap cookies). The crumbs are bound together with softened or melted butter, that firms up when it is refrigerated. It is similar to a cheesecake base or the base used in Nigella's No-Fuss Fruit Tart. Cookies can vary and if the crumb mixture is slightly dry then a little extra butter will usually help to bind it properly. We would mention that the butter should be from a block, as if it is a "spreadable" type of butter from a container then this has added vegetable oil that will keep the butter soft when chilled and will mean that the tart base will not set as well.
It is also important that the biscuits are crushed into small crumbs so that they bind together evenly and pressed firmly into the tart tin. Some people find it helpful to use a potato masher to press the base into place and then a straight-sided glass to press the crumbs into the sides of the tin, or just press very firmly with your fingers or a knuckle.