Sorrel Soup with Torn Croutons

2 T. unsalted butter

2 yellow onions, chopped

9 oz. young, tender sorrel leaves, stems removed

1 1/4 lb. red new potatoes, peeled and thinly sliced

2 cups chicken or vegetable stock, or canned broth

4 cups water

1/2 cup heavy cream

Salt and freshly ground pepper, to taste

Torn Croutons

To make the soup, in a soup pot over medium heat, melt the butter. Add the onions and sauté, stirring, until soft, about 10 minutes. Add the sorrel and cook, stirring, until wilted, about 2 minutes. Increase the heat to high, add the potatoes, stock and water and bring to a boil. Reduce the heat to medium-low, cover and simmer until the potatoes are soft, 15 to 20 minutes. Remove from the heat and let cool slightly.  Using a blender and working in batches, puree the soup on high speed until smooth, 3 to 4 minutes per batch. Strain the puree through a fine-mesh sieve into a clean saucepan. Stir in the cream, mixing well. Season with salt and pepper.  Place the saucepan over medium heat and reheat the soup to serving temperature. Ladle into warmed bowls, garnish with the croutons and serve immediately.