Melt the butter in a large, heavy pot or Dutch oven over medium-high heat. Add the onions, celery, salt and cayenne. Cook, stirring for 5 to 6 minutes. Add the bay leaves and garlic. Cook for 2 minutes. Add the broth and potatoes and bring to a boil. Reduce the heat to medium-low and simmer uncovered until the potatoes are tender, about 30 minutes. Add the sorrel leaves and cook for another 10 to 15 minutes.
Remove and discard the bay leaves and, with a hand-held immersion blender (or food processor or blender in batches) process until smooth. Slowly add the cream, then serve hot.
And if you want to kick it up a notch, add some fresh lump crabmeat. Yum!