Preheat the oven to 180°C (350°F)
Use a small portion of the softened butter to grease the inside of the baking dish.
In a large mixing bowl, whisk together the eggs, white sugar, vanilla extract, cream, milk, mixed spice powder, and orange zest until well combined.
Next, add the cubed bread, sultanas, and nuts to the mixture, use a spatula to gently mix in, and allow the mixture to stand for 5 minutes.
Pour the egg mixture into the greased baking dish and spread out into an even layer.
Drop small amounts of the remaining softened butter over the top of the custard and sprinkle the top with brown sugar.
Place into the preheated oven and bake for 25 - 30 minutes, or until the custard is set but still a little wobbly and the edges of the bread have browned.
Remove from the oven and allow to stand for 30 minutes before serving.
Serve warm or at room temperature garnished with a light sprinkle of powdered sugar or grated orange zest.
Enjoy with a serving of custard, cream, or ice cream.