In a large saucepan over medium heat, add olive oil, sauté leek and onion for 3 minutes. Add potatoes and asparagus, reserve ten tips for garnish. Sauté for 5 minutes. Add stock and simmer until potatoes are tender, about 20 minutes. Working in batches, purée cooled soup in blender or food processor until smooth. Return soup to saucepan and stir in Mrs. Dash® Lemon Pepper Seasoning Blend and lemon juice. Blanch reserved asparagus tips. Ladle soup into bowls, lay asparagus tip on top, garnish with sour cream.