Can I substitute powdered (pasteurized) egg whites for fresh eggs in the Toasted Marshmallow And Rhubarb Cake?
Nigella's Toasted Marshmallow And Rhubarb Cake is a light sponge cake filled with roasted rhubarb and coated with a whisked meringue frosting that is then toasted with a blow torch. The cake uses 6 whole eggs - the yolks are used in the sponges and the whites are used for the frosting. Unfortunately it is not possible to substitute egg yolks with egg whites (fresh or dried) in the sponge layers as egg yolks contain extra fats and without them the cake will be dry and pale.
For the frosting we prefer to use fresh egg whites if at all possible. However if you are unable to eat lightly cooked eggs then we would suggest trying to find pasteurised liquid egg whites to use instead. Larger supermarkets have cartons of these in chiller cabinets (usually in the dairy section) and if you are in the US make sure they are an unseasoned version. Manufacturers of powdered egg whites do advertise them as suitable for meringues. You would need to reconstitute the powdered whites with water, following the instructions on the packaging and making up the equivalent of 6 whites. However as we have not tried powdered egg whites ourselves for this recipe, we are unable to guarantee the results.