Blueberry-Blackberry Crumble

This humble dessert is made velvety by the blueberries, which thicken the sauce. You can also use other berries, such as raspberries, loganberries, boysenberries, or olallieberries, or use all blueberries. Serve with vanilla ice cream, Crème Fraîche, or Barely Whipped Cream.