Preheat the broiler, line a baking sheet, halve the tomatillos, and arrange them with the peppers, onion, and garlic.
Broil the vegetables for about 6 minutes, turn them, and continue cooking until softened and lightly charred.
Allow the peppers to cool, then remove the stems and as many seeds as needed for the preferred heat level.
Transfer all the roasted vegetables to a blender and add the cilantro, lime juice, cumin, and salt.
Blend until smooth, or pulse briefly if a salsa with more texture is preferred.
Cool the salsa, taste and adjust the seasoning, then refrigerate it in a sealed container until serving.
