1. Butter the slices of bread and cut them into triangles.
2. Arrange the slices in layers in an ovenproof dish interspersed with the currants, sugar and lemon zest.
3. Beat the eggs and milk together and pour over the bread. Set aside for about 30 minutes, pushing the bread back down into the milk occasionally.
4. Preheat the oven to 180˚C.
5. Put the dish into a roasting pan filled with hot water and bake for about 45 minutes or until golden and set. Serve dusted with icing sugar.
Try spreading the bread with jam, add chocolate chips or use slices of stale brioche or raisin bread.