Grilling the tomatillos in this salsa adds a lovely smoky flavor and aroma.
Preheat grill or broiler.
Grill or broil tomatillos, turning occasionally, until softened and blackened in spots, 6 to 8 minutes. Core and halve the tomatillos.
Combine the tomatillos, serranos (or jalapenos) and garlic in a food processor or blender; process until smooth. Transfer to a small bowl. Stir in cilantro and lime juice. Season with sugar and salt.
Make Ahead Tip: Cover and refrigerate for up to 4 days.