Preheat oven to 220°C.
Get rid of the tomatillos’ leaves and rince well. Roughly chop the onion. Wrap the garlic in aluminium foil. Lay the tomatillos, onion and garlic on a baking tray, along with the chili pepper, and roast for 15 minutes.
Blend with the coriander, lemon juice and olive oil. Season to salt and pepper.
Leave to cool down in the fridge before serving.