Preheat the oven to fan-assisted 180 C / 200 C / gas 6. (400F)
Mix the berries with the balsamic vinegar and the 2 tbsp of maple syrup and transfer into a ceramic baking dish. Use a small dish so that the berries roast in their liquid (otherwise the liquid might evaporate).
Roast for about 20 minutes, turning half way through, until the juices are bubbling and the berries start to turn darker.
Then remove the berries from the oven and allow to cool.
When cool, transfer the roasted berries and their juices along with all the other ingredients, including extra maple syrup if desired, into a blender and whizz until well combined.