I have a family recipe for a to-die-for hazelnut torte with chocolate frosting. I want to bake it for an occasion coming up, but there will be at least two, possibly three people there who are allergic to chocolate. (No, none of them are related to each other. Just one of those things.) What sort of frosting can I make that will go well with the hazelnut, but which doesn't involve chocolate?
The cake is pretty sweet — equal parts sugar and ground hazelnuts, plus egg whites — so I usually make a bittersweet chocolate frosting by combining a good half or two-thirds cup of dutch cocoa with 2 or 3 tablespoons of sugar, 6 tablespoons water, and 8 egg yolks, cooking until thickened, and when cooled mixing it with two sticks of unsalted butter. I'm thinking if I leave out the cocoa, I will have to substitute something for the volume as well as the flavor.
I often see raspberries paired with hazelnuts and chocolate. Do raspberries still go well with hazelnuts if there is no chocolate involved? Also, unsweetened raspberries tend toward the sour, while unsweetened chocolate is bitter; how would that affect things?