Blackberry and Apple Cake Recipe
Joyce Park stashed this in Food
There two fruits are rarely ripe at the same time in my experience, but if you can bring yourself to use out of season fruit this sounds delightful.
It's a strange combination for that very reason that one is always out of season from the other.
But it does sound delightful.
Frozen fruit is also a possibility...
Must be an American thing... in the UK, blackberry and apple seasons are pretty much bang on the same time, so blackberry and apple combinations are pretty common - http://www.bbcgoodfood.com/recipes/778642/apple-and-blackberry-crumble