In a soup pot, saute the onions and potato in the butter, turn down the heat, cover and let cook on low for about 7 mins
Add the broccoli and cook another 5 mins
Increase heat and add stock, bring to a boil then simmer 15-20 minutes
Add the vegetables and one cup of stock to a food processor and process til smooth, adding the remainder of the stock as you go
Return the soup to the pot and put it back on the stove on very low. Add the mace, salt and pepper and then slowly stir in the cheese til itu2019s fully melted in.
Serve with croutons