Here's the recipe from Martha's Stewart's Everyday Living.... (I halved it for my family)
Christmas Tree Soup
1 Tbsp olive oil
1 med onion, diced
coarse salt & pepper
2 cans chicken broth
1 large head broccoli (3#), peeled, chopped
1 med baking potato, peeled and chopped
1/2 cup heavy cream
1/4 cup lemon juice
Saute the onion in oil, season with salt and pepper. Cook until soft. Add broth, broccoli, potato and 2 cups water. Bring to boil and simmer until tender. Puree soup and return to pot. Stir in cream and lemon juice, season with salt and pepper.
(my changes: for a half the recipe use 2 cups water and 2 chicken bullion cubes for the liquid and keep the full amount of cream!)