Poblano Chile Sauce from The Hog Island Book of Fish & Seafood: Culinary Treasures from Our Waters by John Ash

Ingredients

• 1 small white onion, sliced
• 2 tablespoons canola or other neutral oil
• 4 large poblano chiles
• ½ teaspoon ancho chile powder
• ½ teaspoon dried oregano, preferably Mexican
• 1 teaspoon thinly sliced garlic
• ⅓ cup (75 ml) chicken stock or vegetable stock, or more as desired
• ½ cup (120 ml) crème fraîche or Mexican crema
• Fine sea salt and freshly ground pepper