Turn your oven on to 200c (180c fan)
Heat the oil in a medium-sized pan over a low heat. Add the finely diced onion and sauté until soft and translucent.
Add the garlic and continue to cook for 2 minutes. Stir often to prevent the garlic and onion from burning.
Add the spinach and allow to wilt down for a few minutes. Once wilted remove from the heat.
In a jug combine the cornflour with a small amount of the milk taken from the half pint. Stir to form a paste.
Pour the rest of the milk into a small saucepan along with the bay leaf and the nutmeg (if using). Heat until it comes to a simmer.
Remove the bay leaf and whisk into the cornflour mixture. Return the whisked milk back to the pan and cook on a moderate heat, stirring continuously until it thickens and becomes smooth.
Remove from the heat and season with salt and a good grind of black pepper then add most of the parmesan cheese.
Tip the wilted spinach mixture into the cheesy sauce and mix well.
Spoon into an oven proof dish, sprinkle with the remaining cheese and bake for 20 minutes or until the cheesy topping is golden brown and the creamed spinach is bubbling.
Allow to cool slightly before serving.