Rinse and dry the fresh cilantro, then remove the stems. There's no need to chop it, as it will be blended, just use the leaves.
Remove the husks from the tomatillos and rinse them thoroughly to remove the sticky residue. Then, slice them in half and place them cut-side down on a sheet pan lined with parchment paper.
Add the sliced onion, sliced and seeded jalapeño, and unpeeled garlic cloves to the pan. After that, lightly spray with oil and sprinkle with 1/4 teaspoon of salt.
Set your oven to broil and place the sheet pan on the top rack. Broil for 5-7 minutes or until the tomatillos are nicely charred.
Flip the tomatillos, onion, and pepper, and broil for another 2-3 minutes or until charred on the other side. Then, remove the sheet pan from the oven and let the roasted ingredients cool slightly.
Peel the roasted garlic cloves and add them to a food processor or blender. Then, add the roasted tomatillos, onion, and jalapeño. After that, toss in the fresh cilantro leaves, fresh lime juice, and remaining 1/4 teaspoon of salt.
Blend the tomatillo salsa until smooth. Enjoy this salsa verde warm or chilled. It pairs perfectly with tortilla chips, tacos, grilled meats, or as a sauce for enchiladas.