Butter the bread and cut each slice into quarters.
With the buttered sides uppermost, arrange the quarters over the bottom of the ovenproof dish, overlapping them to fit.
Scatter the currants, sultanas and mixed peel on top.
Then in a separate bowl, whisk together two of the eggs and the yolk only of the third. Whisk in the sugar and then stir in the milk and vanilla extract.
Strain the custard and then gently pour over the bread.
Sprinkle the top with the cinnamon and demerara sugar, and then leave for 30 minutes.
Meanwhile preheat the oven to 180°C (350°F) (gas 4)
Put the dish into a roasting tin/pan and then fill the roasting tin/pan with boiling water until it comes half-way up the sides of the dish. Bake for 45 minutes until the custard is set and the top is brown and crispy.