I came up with this cake to use up little bits of things I had laying around: blueberries, white chocolate, buttermilk and limes. And I gotta say, I love this cake. A hint of buttermilk and white chocolate in the light cake with a crispy crusty "bottom", enriched with an sweet and sticky brown sugar-blueberry-lime "top." If you are not a huge fan of very sweet desserts, you may want to reduce the brown sugar in the topping to 1/2 cup or so. It is phenomenal served with a scoop of homemade vanilla ice cream!