In large heavy saucepan, heat oil and sherry until bubbling.
Add onion and saute 5 minutes -(If mixture appears dry, add 1-2 teaspoons water.)
Add carrot, celery, bay leaf, potatoes and stock.
Cover, bring to boil and cook over medium heat for 10-15 minutes, or until potato is tender.
Add milk and corn then simmer for 3 minutes or until corn is tender.
Puree 1 cup soup in blender, then return to pot and season with cayenne.
If desired, garnish with yogurt.
Note: Go easy on the cayenne; the first time I made this I overdid it!