Photograph: Laura Edwards
In a bowl, mix together the grated zest of 1 orange with the butter. Spread one side of each slice of bread with a thick layer of butter, then spread 4 of the slices on the back with the marmalade. Sandwich the marmalade slices of bread together with the other slices to make sandwiches, then cut each into 4 triangles. Arrange in a 1.5 litre ovenproof dish.
Cut the ungrated orange in half; cut half into 8 thin slices; then cut these into quarters. Put in a heatproof bowl with 3 tablespoons water, cover with clingfilm and microwave (800W) on high for 2 minutes. Leave to cool. Squeeze the juice from the grated orange and the ungrated orange half into a jug. Whisk in the cream, milk, eggs and sugar. Pour over the pudding; set aside for 30 minutes.
Preheat the oven to 180°C, fan 160°C, gas 4. Drain the liquid from the orange slices and scatter them over the top of the pudding, along with the chocolate chips. Sprinkle over the demerara sugar and bake for 30 minutes until golden and crispy.
Get ahead: prepare up to the end of step 2 up to a day ahead, cool, cover and chill.