POTATO LEEK SOUP WITH TARRAGON

Ingredients

• 3 T butter
• 2 large leeks (white and pale green parts only), sliced (about 2 cups)
• 1 small onions, chopped
• 4 garlic cloves, sliced
• 2 T water
• 1/2 pound potatoes, unpeeled, cut into 1/2-inch pieces
• 4 C low-salt chicken broth or vegetable broth
• 1 t chopped fresh tarragon
• 1/4 C heavy cream
• 1/4 C sour cream
• salt and pepper, to taste