Gently bring 500ml whole milk to the boil in a small saucepan with 1 halved onion, studded with 1 bay leaf and 2 cloves. Turn off the heat and leave to infuse for 20 mins.
Melt 50g butter in another saucepan, then add 50g plain flour. Stir continuously until a paste forms – this is called a roux. Continue cooking for 2 mins.
Remove the onion, bay and cloves from the milk with a slotted spoon and discard. Add the infused milk to the roux gradually, stirring as you go, until you get a smooth sauce. Cook for 5-10 mins, stirring continuously, until the sauce has thickened. Season to taste.
Calories (kcal) 416
Protein (g) 13
Fat (g) 16
Carbohydrate (g) 57
Vitamin A (mcg) 161
Vitamin C (mcg) 15