Shall we say: I like lemon cake (or lemon cakes)
and: I want some lemon cake (or lemon cakes)?
Both sentences are correct, though, I'd probably prefer the singular with the latter "I want some lemon cake" if your intention is to eat one right now. Unless you mean the smaller kinds of lemon tarts you must be very hungry to want more than just one lemon cake
Perhaps you are hoping to buy several?