For cinnamon-roasted rhubarb, preheat oven to 150C. Place rhubarb in an ovenproof dish, scatter with sugar and cinnamon, drizzle with Marsala and roast until tender (30-40 minutes). Cool.
Combine egg yolks and 100ml rhubarb cooking liquid in a heatproof bowl over a saucepan of gently simmering water and whisk until pale and tripled in volume and mixture holds a trail (8-10 minutes). Cool and serve spooned over rhubarb with cantucci to the side.