Heat oil in a heavy saucepan. Add onions, garlic and poblano chilies; sauté until just tender. Deglaze pan with dark beer; allow mixture to reduce by half. Add ancho chilies, chipotle puree, tomato and tortillas; simmer 30 minutes over medium heat. Add spices, then season to taste. Pureé mixture, then set aside in a warm place.
Heat butter in a skillet; sauté rock shrimp. Add shrimp to chili; heat together. Season to taste. Pour into bowls, then garnish with sour cream, lime juice and cilantro sprigs.
Makes: 4