Put the sultanas into a small bowl and cover with the fruit juice, sherry or brandy. Set aside to soak.
In a small bowl, mix the cornflour to a paste with a little of the dairy-free milk until it is completely smooth.
In a saucepan, heat the remaining milk, dairy-free cream, sugar, vanilla extract, a grating of nutmeg and lemon zest. Stir in the cornflour paste and keep stirring over a gentle heat until the custard has thickened a little. Set aside until needed.
Grease a baking dish with vegan butter.
Butter each slice of bread with vegan butter, and slice into quarters.
Arrange about two-thirds of the bread pieces in the baking dish, scattering over all of the sultanas as you go. Pour two-thirds of the custard over the bread and set it aside to soak for 20-30 minutes.
Preheat the oven to 180°C / 350°F / Gas Mark 4.
Arrange the remaining bread pieces on the top of the pudding then cover with all the remaining custard. Scatter over the demerara sugar.
Place the baking dish in a roasting tin and fill it half way with boiling water to make a bain-marie.
Bake the pudding for 35-45 minutes until the top is crispy and golden brown and the custard is bubbling.