Preheat oven to 350 and grease and 8 x 8 baking pan.
In a small bowl, toss the blackberries with the balsamic. Set aside.
In a medium sized bowl, beat the olive oil with the egg until frothy. Whisk in the sugar. Sift in the flour, baking powder and baking soda and gently fold to combine. Add the milk and use a wooden spoon to fully incorporate.
Fold in half of the raspberries and vinegar. Pour the batter into the prepared pan. Dot the batter with the remaining berries and drizzle with remaining juices.
In a small bowl, mix together the streusel ingredients to form a crumbly mixture.
Sprinkle with batter with the streusel and bake for 35 minutes, or until a toothpick inserted in the center of the cake comes out clean.
Serve warm with a cup of hot tea or coffee and drizzle with Raspberry Balsamic Vinegar.
