First, put the oat flakes in a saucepan with the custard powder, cocoa powder, water and milk.
If you like, you can add a little maple syrup to sweeten.
Bring the pudding oats to the boil and stir well with a whisk until the mixture starts to thicken. At first the mixture will still be very runny, but after a few minutes it will gradually thicken.
When the mixture starts to thicken, turn off the heat and stir for 1 minute more.
Then take the pudding oats off the heat and leave them to stand for another 2 minutes or so.
You can use different nuts or seeds as toppings. We used walnuts and cocoa nibs, as well as some almond paste as toppings for the pudding oats.