Cream of Almost any Vegetable Soup

1/2 cup (1 stick) unsalted butter, olive oil, or safflower or other high-quality vegetable oil
2 cups chopped onion or leek, including pale green portion of leek
2 pounds asparagus or other raw vegetable, trimmed and cut into small pieces
3 cups vegetable stock, poultry stock, or canned chicken broth, preferably low-salt type
1 cup heavy (whipping) cream
Salt
Freshly ground white pepper
Sliced blanched asparagus or fresh herb sprigs, for garnish
Pesticide-free, non-toxic flowers such as lilac, for garnish (optional)


In a soup pot or large, heavy saucepan, melt the butter or heat the oil over medium heat. Add the onion or leek and sauté until golden and very soft, about 30 minutes. Add the asparagus or other vegetable and sauté for about 5 minutes. Add the stock or broth and bring to a boil over medium-high heat. Reduce the heat to low, cover partially, and simmer until the vegetable is very tender, about 25 to 45 minute, depending on the type, size, and age of the vegetable. Remove from heat and cool slightly. Working in batches, if necessary, transfer the soup to a food processor or blender and puree until smooth. Strain through a medium-mesh sieve into a clean pot, if serving the soup hot, or into a large bowl, if serving the soup cold; with a large spoon, press the vegetable pulp against the sides of the sieve to release as much liquid as possible. Stir in the cream and season to taste with salt and pepper. To serve hot, heat over medium-low. Ladle into preheated soup bowls, garnish with asparagus or herb sprigs and flowers, if using, and serve immediately. Alternatively, pour into a container and refrigerate, uncovered, until cool, then tightly cover and store for up to 3 days. Slowly reheat before garnishing and serving. To serve cold, pour into a container and refrigerate, uncovered, until cool, then tightly cover and chill for at least 2 hours or up to 3 days. Ladle into chilled bowls and garnish as for hot soup.