Grilled Asparagus with Creamy Pasilla Chile - Rick Bayless

Ingredients

• 2 tablespoons olive oil (plus a little more for the pasilla and asparagus)
• 1 medium onion, sliced ¼-inch thick
• 4 garlic cloves, peeled and finely chopped
• 3 medium (about 1 ounce total) dried pasilla (negro) chile, stemmed and seeded
• 1/2 cup Mexican crema or crème fraiche
• Salt
• 1 teaspoon vinegar—practically any kind will work here, though a dark one like balsamic will underscore the pasilla flavor
• 1 large bunch (about 1 pound) asparagus