Begin by preheating the oven to 350℉ (175C/155C Fan) and lightly greasing a 9" casserole dish with butter.
In a mixing bowl, stir together all the filling ingredients - the cherries, blueberries, cornstarch, cinnamon, brown sugar and lemon juice. Add the mixture to the greased casserole dish and set aside while you prepare the batter.
In a separate mixing bowl, whisk together the egg, milk and vanilla extract.
Then add the flour, sugar, cinnamon, baking powder and salt and whisk until smooth, removing any lumps.
Add the melted butter and whisk lightly to combine.
Pour the batter over the berries in the casserole dish.
Bake in the centre of the preheated oven until the batter is golden and the filling is bubbling up around the edges. You can test the doneness of the batter with a toothpick to ensure it is baked through.
Remove from the oven and serve with ice cream.