Remove the skins from the broad beans. Thinly slice the onion. Peel and slice the potato, then soak it in water and drain.

Heat butter in a pot over low heat. Once half melted, add the onion and sauté until softened. Add the potato and broad beans, stir to coat with butter, then add water, consomme, and bay leaf. Cover and simmer for 10 minutes until the potato is tender.

Remove the bay leaf from the pot and blend the mixture until smooth using a blender.

Return the blended soup to the pot, add milk and salt, and adjust seasoning. Transfer to a bowl and chill in the refrigerator for 1 hour.