Heat butter in a 4 quart saucepan. Saute onion for about 5 minutes or until tender. Add the pumpkin and bring to a simmer until you are ready to eat. (Note that if the soup is too thin, you can soak the bread in some more broth and when tender, add it to the soup) Season to taste with salt and pepper and a very fine touch of ground mace. Right before serving, remove the hot soup from the heat and add the cheese. (For company you can whisk in some heavy cream before serving or top the soup with sour cream). Garnish with snipped chives.