1 pound asparagus, trimmed and chopped (reserve woody ends)
3 tablespoons olive oil
4 cloves garlic, minced
3 small leeks, white and light green parts, chopped and washed
2 tablespoons all-purpose flour
1 1/2 teaspoons salt
1/2 teaspoon freshly ground black pepper
1/4 cup lemon juice
Put the broth and woody asparagus ends in a small saucepan. Simmer for 15 minutes, to infuse the broth with asparagus flavor.
While the broth simmers, heat the oil in a large pot, add the garlic and leeks, and sauté over medium heat for 10 minutes. Add the flour and stir continuously for 2 minutes to make a light roux.
Remove the woody stems from the broth with a slotted spoon and discard them. Pour the broth into the large pot with the leeks and garlic. Add the raw asparagus and simmer for 10 minutes, or until the asparagus is bright green and tender. (Don’t cook it so long that it becomes dark and mushy.)
Remove from the heat, and with an immersion blender or in an upright blender, puree in small batches until completely smooth.
Season with salt and pepper and stir in the lemon juice.