Preheat your oven to 425°F (220°C).

Remove the husks from the tomatillos and rinse under cold water. Chop the onion and slice the jalapeño. Place on a baking sheet.

Roast the vegetables for 20-30 minutes until soft and golden.

Let the vegetables cool for about 10 minutes.

Transfer the cooled vegetables to a blender and add garlic and salt. Blend until smooth.

If using cilantro, stir it in now and pulse a few times to combine.

Taste the sauce and adjust seasoning as necessary.

Use immediately or store in a container for up to 5 days in the fridge or freeze for up to 2 months.