Basic Cream of Vegetable Soup

1/2 cup (1 stick) unsalted butter, olive oil or other good oil
2 cups chopped onion or leek, including pale green portion or leek
2 pounds asparagus, broccoli, cauliflower or other raw vegetable, cut into small pieces
3 cups vegetable stock
1 cup heavy (whipping) cream (or substitute light cream, half and half, low fat milk, low fat yogurt or buttermilk)

Melt butter or heat oil over medium heat
Add onion or leek and saute until golden and very soft, about 20 minutes
Add vegetables and saute for about five minutes
Add stock or broth and bring to boil over medium high heat
Reduce heat to low, cover partially and simmer until vegetable is very tender, about 25-45 minutes depending on type
Remove from heat and allow to cool slightly
Working in batches if necessary, transfer soup to food processor or blender and puree until smooth
Strain through medium mesh sieve into clean pot, pressing vegetable pulp to release as much liquid as possible
Stir in cream and season to taste with salt and pepper