This brightly acidic, cumin-spiked hot sauce is an excellent condiment for any Mexican-inspired meal. To give the sauce kick, we use a serrano chili with its seeds, but you could remove the seeds for less heat. For an even milder sauce, replace the serrano with a seeded jalapeño. Stored in an airtight container in the refrigerator, the sauce will keep for up to a week.
Don't worry if the vegetables broil somewhat unevenly. The chilies may brown the most and the tomatillos should be fully softened, but be careful not to scorch the garlic. And don't worry about removing the charred skins before processing—they add a subtly smoky flavor.