In a large saucepan, bring the stock to a boil.
Add the artichoke hearts and asparagus and cook for 3 minutes, or until the asparagus is almost tender.
Add the spinach and cook for 1 minute, or until it turns soft and bright green.
In a small cup, beat the egg.
Slowly and gently stir the egg into the soup, cooking just until thin threads form
Stir in the lemon juice; add salt and pepper to taste.