Rich Cream of Asparagus Soup
Remove the tips from the asparagus and set aside. Snap off the tough bottoms from the stalks and discard. Cut the stalks into 1-inch lengths and set aside.
In a large saucepan, heat the butter and in it sauté the leeks over moderately low heat until tender. Add the garlic for the last minute of cooking.
Add the asparagus stalks, potato, and enough stock to cover the vegetables and bring to a boil. Lower the heat and simmer, partially covered, until the vegetables are tender, about 30 minutes.
While the vegetables are cooking, bring 2 cups water and 1/2 tsp salt to a boil in a small saucepan. Add the asparagus tips and cook until just tender, about 5 minutes, Drain and set aside on paper towels.
When the vegetables in the stock are, tender, purée the mixture in a food processor or food mill.
Return the purée to the saucepan. Add the remaining stock, bring to a simmer, and remove from the heat.
In a small bowl, beat egg yolks into the heavy cream and whisk in 1 ladleful of the hot soup. Whisk this mixture into the hot soup and cook over low heat, stirring constantly, until the soup thickens. Do not allow the soup to boil or the eggs will curdle. Add salt and pepper to taste.
When the soup has thickened, stir in the lemon juice and the asparagus tips. Serve in heated bowls.