Chocolate Berry Cake with Berries as main batter ingredient?

I have this rather vague idea that popped into my head for a chocolate berry cake of some kind where the berries, pureed, go into the batter itself and form a large proportion of the ingredients.

Unfortunately, I lack the knowledge of how cakes 'work' to be able to figure out how to make this, and everyone I've talked to so far has never heard of anything like my idea.

Is such a cake feasible, and can anyone offer any suggestions on what such a cake might need, ingredients- and preparation-wise?