Preheat the oven to 375 degrees F (190 degrees C/gas 5). Put the fruit into a pan with the sugar and the balsamic vinegar. Put the pan over the heat, and cook gently, until the juices begin to run from the berries. Pour into an ovenproof dish.
Meanwhile make the topping. Rub the cold butter into the flour until the mixture resembles fine bread crumbs. Add the sugar and salt, stir well, and then add the buttermilk to form a loose, scone-type mixture. Roll balls of the dough and place randomly over the hot fruit. Sprinkle with a little sugar, and bake in the oven for 30 minutes until golden brown. Serve with vanilla ice cream.