I made one of Nigella's pavlovas today, Sunday, and still have the yolks. I was thinking of making her Creme Brûlée for Tuesday but can I mix egg yolks and sugar and leave them in the fridge until Tuesday before making the custard mixture.Will the egg yolks keep?
Egg yolks usually keep for 2-3 days as long as they are kept refrigerated. You should also cover them tightly as they tend to absorb other flavours/smells easily and this could affect the flavour of the Creme Brulee.
We would recommend just refrigerating the yolks as they are and not adding the sugar to them until you are ready to make the custard. The reason for this is that if you mix sugar with egg yolks and let them stand then the yolks will form hard lumps (some people refer to this as the sugar "cooking" the yolks). The actual chemical reaction that occurs is that the sugar attracts water from the yolks and this causes the proteins in the yolks to clump together and become hard. Unfortunately once this has happened it can't be rescued and you would have to throw the mixture away.