I would like to bake an Opéra cake for someone who doesn't really appreciate the taste of coffee. Since coffee and chocolate are the two main elements, I am wondering: what flavour could I substitute for coffee in my coffee buttercream? I suppose the qualities I'm looking for are a bit of bitterness, and it should go well with chocolate and orange liquor?
PS: I just noticed that the English wikipedia describes the sponge cake as “soaked with coffee”, but in the way I usually do it it's soaked with Cointreau so I don't need any replacement there.