Stir the oats and cinnamon in a saucepan together, then pour over the milk. Bring to the boil and gently simmer for 10 minutes, until creamy.
Turn off the heat, stir, put the lid on, then rest for about 10 minutes.
Meanwhile, peel the roasted chestnuts and put aside 4 of them, then chop the rest. Spoon some porridge into four glasses or small pots, then scatter some chestnuts over it, then top with vanilla custard or yoghurt.
Repeat once more the layering (porridge, chestnuts, custard) then add some whipped cream and put a chestnut on top of each.
Serve immediately.