• 3 tablespoons unsalted butter
• 1 pound onions, coarsely chopped
• 1 small garlic clove, minced
• 6 cups chicken stock
• ½ pound potatoes, peeled and coarsely chopped
• ¾ pound sorrel, trimmed and torn in large pieces
• salt and freshly ground pepper, to taste
• sour cream

Heat butter in a deep pot and sauté onions until wilted and turning golden, about 5 minutes.  Add garlic and cook for another minute.  Add stock and heat, then add potatoes. Simmer until potatoes are done, about 10 minutes.  Stir in sorrel and heat thoroughly.
Transfer to a food processor and puree.  Return to the pot and heat for another few minutes, correcting seasoning with salt and pepper if necessary.