For the fruit, put all the ingredients in a saucepan. Cook over a low heat, stirring until the butter has melted and the sugar has dissolved, then leave to simmer until you have a chunky fruit compote, then set aside.
Heat oven to 190C/170C fan/gas 6. Whisk the egg into the milk and set aside. Rub the butter and the flour together until it has the texture of chunky breadcrumbs, then stir in the caster sugar, cinnamon, baking powder and a large pinch of salt. Pour in the milk mixture and bring together to form a thick, batter-like texture.
Tip the compote into a baking dish and top with large spoonfuls of the cobbler mix, making sure there are a few gaps for the fruit to bubble through, then sprinkle everything with the demerara sugar. Bake for 35-40 mins or until the topping is golden and just cooked through. Remove from the oven and leave to rest for 5 mins before serving straight from the dish with generous spoonfuls of clotted cream.