Cut broccoli into florets and slice stems. Cook broccoli in boiling, salted water until just done, firm and very green. Reserve a few florets of broccoli for garnish.
Place the broccoli into a pan with the butter and minced onion. Cover and steam for 10 minutes. Stir once or twice, do not brown.
Add the stock and rice, bring to boil, lower the flame and simmer 30 minutes.
Strain through a fine sieve, forcing the vegetables through. Return to kettle add the cream, butter, nutmeg and pepper. Heat again and serve with the reserved florets as garnish.
To make this soup in a blender, after simmering broccoli in the stock, add to the blender (you many need to split the soup into multiple portions) and blend until a smooth puree is obtained. Return to kettle, add cream and butter, season and heat.
Serve with a little salted whipped cream, if desired, and the broccoli florets on top.