Preheat the grill to its highest setting.
Place the milk into a saucepan over a medium heat. Add the onion, peppercorns, bay leaves and thyme and bring to the boil to infuse the flavours.
Remove the pan from the heat, cover with a lid and allow the milk to stand for 10-15 minutes. Strain the milk through a sieve into a bowl and discard the solid ingredients.
Place the low-fat spread into a clean saucepan over a gentle heat. Once melted, add the flour and cook, stirring well, for 2-3 minutes.
Add the infused milk, stirring all the time and bring the sauce gradually to the boil.
Season with salt and freshly ground black pepper, then allow the sauce to simmer for 3-5 minutes, stirring occasionally.
Meanwhile, cook the macaroni according to packet instructions. When it is just cooked, drain and place into a warm earthenware or heatproof dish.
Add 110g/4oz of the grated cheddar cheese and all of the chopped parsley to the white sauce, stir well, then pour this over the cooked macaroni.
Cover with the remaining grated cheese and place the dish under the grill to cook for 5-7 minutes, until the cheese is bubbling and golden-brown.
Serve at the table in the dish.
