Scatter the sliced rhubarb in a 25cm (10in) square ovenproof dish or a similar-sized dish, and sprinkle over half (75g (2½ oz)) of the caster sugar. Toss together and then leave the rhubarb to sit for about 30 minutes to soften a little.

Preheat the oven to 180°C, 350°F, Gas 4. Butter the slices of white bread and arrange four slices, butter side down, in the ovenproof dish. Scatter over half of the sliced rhubarb and top with four more slices of bread, again with the butter side down. Repeat with another layer of sliced rhubarb and another layer of buttered bread, then add a final layer of sliced rhubarb and finish with a layer of buttered bread, ensuring that the bread is placed with the buttered side down.

Put the cream and the milk in a saucepan and bring it just to the boil. While it is coming to the boil, in a bowl, whisk the eggs, the pinch of salt and the remaining 75g (2½ oz) of caster sugar. As you continue to whisk, pour the hot cream and milk mixture into the egg, salt and caster sugar mixture until it is well mixed. Pour this custard over the slices of bread in the dish and leave to soak for 10 minutes. Sprinkle the granulated sugar over the top.

Put the dish into a deep-sided baking tray and pour in enough boiling water to come halfway up the sides of the dish (this is known as a bain-marie). Put it in the oven to bake for 45-50 minutes or until it is just set in the centre. Remove it from the oven and serve with a light dusting of icing sugar and softly whipped cream.