Im not sure i'd find the combo appealing but let us know how it goes! I prefer orange much more than lemon as fruit to pair chocolate with. Would you consider maybe a white chocolate cake? That seems like something that would go better with the lemon curd. Just my 2 cents.
Oooh, now Thornton's Lemon Parfait chocolates are my favourite and these combine a lemon filling encased in dark chocolate and they are divine, so don't knock it until you've tried it I say!
I love chocolate with citrus.
My favorite cake is yellow cake with lemon curd filling and chocolate frosting.
I'd definitely enjoy chocolate cake with lemon filling. Delish!
Im glad you ask this question because I have been wondering the same thing. I know that I love a Hershey Chocolate Bar with a Mello Yello soda so Im thinking about trying this. I just purchased a jar of lemon curd the other day so if I try it I will let you know how it turned out. 
I worked at a commercial bakery a number of years ago and the chocolate/lemon combo was quite popular. Kinda like eating a cocolate covered lemon. It's good though.
What's the orange marmalade for?
I usually strain mine and use it as a wash on some cakes.
If your gonna use the orange marmalade as a filling, you might want to keep the rind. If not, you'll need to warm the marmalade up then strain it through a metal strainer, then spread it out after it cools completely.
I usually use it to brush it on all over the cakes before icing and filling.
LOL
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