Preheat your oven to 425°F (220°C). Husk and rinse tomatillos, quarter the onion, and set garlic aside.

Arrange tomatillos, onion, and garlic in a baking dish in a single layer. Add jalapeños if desired.

Roast the vegetables for about 15-20 minutes, stirring occasionally, until tender and slightly charred.

Remove from oven and let cool for a few minutes. Peel the roasted garlic.

In a blender, combine roasted tomatillos, onion, garlic, jalapeños, and cilantro. Squeeze in lime juice and blend until smooth.

Taste and add salt as needed. Add olive oil for richness, if desired, and blend briefly.

Transfer salsa to a serving bowl. Chill for at least an hour before serving for better flavor.