I have a couple of recipes for cakes that require two whole oranges to be boiled and then put into a food processor and blitzed before adding the rest of the ingredients. I'd like to know why the oranges need to be boiled if they are going to be processed anyway? Is it to do with taste, texture or simply ease of processing?
For a boiled orange cake the oranges are boiled for a couple of reasons. Boiling the oranges softens the peel of the oranges and makes them easier to chop finely in a food processor (or by hand). Also boiling the oranges tends to mellow the pith of the orange (the white part of the skin) - the pith tends to be quite bitter and could leave an unpleasant taste in the cake if it was used raw.
We also suspect that if raw pureed oranges were used it would lead to hard chunks of orange skin in the cake. The baking time of the cake would generally not be enough to soften any larger chunks of orange skin and also the sugar in the cake could harden the skin slightly as well (this tends to happen in marmalade making if the sugar is added before the orange peel has softened sufficiently).
If you don't have time to boil the oranges and make the cake on the same day then you can boil the oranges 1-2 days in advance. Transfer the boiled oranges to a bowl and let them cool (reserve the liquid if it is needed in your recipe) then cover and refrigerate them for 1-2 days before using as directed in the recipe. For best results bring up to room temperature before using.