In a covered pot, simmer the onions and the potatoes in the melted butter for 5 minutes. Add the broccoli and cook for another 5 minutes. Cover with water and bring to a boil. Add a pinch of salt and let simmer gently for 15 minutes.

Strain the soup through a sieve or colander, setting aside the liquid for later use. Put the vegetables into a blender and moisten with a little of the reserved liquid. Blend long enough to obtain a velvety smooth puree. Add in the rest of the reserved liquid without turning off the blender. Return the blended soup to the pot and heat just long enough to reach a boil. Remove the pot from the heat.

Add the Blue cheese cubes and stir gently until it melts. Add the pepper, nutmeg and salt to taste. Pour the soup into warm bowls and garnish with a dash of walnut oil.