8 fresh pasilla or poblano peppers
2 tablespoons butter
3 cups fresh or frozen, thawed, corn kernels
3 green onions, sliced, including green tops
1 tablespoon chopped fresh oregano leaves or 2 teaspoons dried oregano
1 cup Mexican crema or sour cream
1/4 cup crumbled Mexican cotija or grated Parmesan
Salt and pepper
1/2 pound small cooked shrimp, optional