Pineapple Salsa for Lamb Burgers

Toast pasilla chiles in a dry small skillet over medium-high heat, turning often, until skins begin to blister, about 3 minutes.

Heat oil in a medium saucepan over medium heat. Add onion and garlic; season with salt and pepper. Cook, stirring, until onion is translucent, 4 to 5 minutes.

Add toasted chiles, the pineapple, sugar, vinegar, mustard, and chipotle chiles to saucepan. Cover; simmer until pineapple is translucent, about 15 minutes. Discard pasilla chiles. Refrigerate salsa until cold, about 1 hour, before serving.