Preheat your oven to 200°C/180°C fan/gas mark six.
Roughly cut your rhubarb into 6cm chunks. Place into a baking tray and cover with 50g of caster sugar and half the orange zest.
Squeeze over the orange juice from one orange, and toss the rhubarb to coat it well.
Arrange the rhubarb in a single layer, cover the tray with foil, and roast for 15 minutes.
Reduce the oven temperature to 180°C/160°C fan/gas mark four and grease a baking dish with butter.
Smother a thin layer of custard in your tray.
Cut your croissants in half lengthways and arrange them in the baking dish, cut-side up.
Spoon a generous amount of roasted rhubarb over the croissants, saving about half for later.
Add the other half of your croissants, top side up.
Pour your custard mixture over the top, exposing the croissant tops.
Scatter the remaining rhubarb loosely on top.
Let your pudding sit for 30 minutes to absorb the rhubarb syrup & custard.
Bake for 20 minutes until you notice a bit of color on your pudding.
Spoon over the remaining rhubarb and its syrup, grate over the remaining orange zest, and dust with icing sugar.
