Preheat the oven to 180C/350F and grease your baking dish with the spoon of butter.
Place the cubed bread, apples, and blackberries in the dish and toss them together.
Sprinkle the sugar, cinnamon and salt on top of the bread and fruit and then mix in well with a wooden spoon. Spread everything into an even layer in the dish.
In a mixing bowl, whisk the eggs, cream and milk until smooth.
Pour over the bread and fruit in the baking dish. The milk and egg mixture should just barely cover the ingredients. If necessary add a little more milk here and there.
Transfer the baking dish to the oven and bake for about 25 minutes until the custard is set (check the middle with a spoon to make sure) and the top is golden brown.
Serve hot or warm with a drizzle of raw cream and some blackberries sprinkled on top if you like.