Melt butter in stock pot; add celery and onion. Cook vegetables until translucent. Over low heat, add flour to make a roux. Cook roux for 3 minutes until blonde in color. Add shrimp stock and bring to low boil. Add cayenne, Old Bay, salt and pepper. Add potatoes and simmer until potatoes are tender, about 30 minutes. Add heavy cream and tomato puree; simmer to bring to desired temperature. Add conch and adjust seasoning. Simmer until conch is heated through. Serve in soup crock topped with sliced scallions and a side of oyster crackers.