Heat the butter in pan over a medium heat until just starting to sizzle, then continue to cook until it turns a nutty brown. Add the onion and bay leaf, if using, and cook over a low heat for 10-15 mins until the onion is soft and lightly golden. Add the milk and ground spices, then season and bring to the boil. Remove from the heat and set aside to infuse for at least 5 mins. Can be made a day ahead and chilled.

Remove the bay leaf if needed, and add the bread. Bring back to the boil, then remove from the heat and blitz using a hand blender or blender until smooth. Return to the pan and simmer gently for 2 mins until thick. Can be made a day ahead and chilled, then reheated with a splash more milk. Tip into a bowl and season with black pepper before serving.