Preheat broiler. In a 4-quart Dutch oven heat butter and olive oil over medium-low heat until butter is melted. Add Vidalia onion slices; stir until coated. Cover; cook 15 minutes until translucent and soft, stirring occasionally.

 Stir in leek and green onions. Cook, covered, 10 minutes more or until leeks are softened.

 Stir in peas. Add chicken broth, water, pasta, and salt. Bring to boiling. Reduce heat. Simmer, uncovered 5 minutes. Stir in lemon juice and basil leaves.

Top slices of sourdough bread with fontina cheese. Arrange on a baking sheet. Broil 3 to 4 inches from the heat for 1 to 2 minutes or until cheese is melted. Top soup with bread slices. Serve with Lemon Sour Cream Topper.