Preheat the broiler in the oven and move the oven rack to just under the heating element. The rack should be close to the heating element but the ingredients should not be touching it. If they are, move the rack to a lower option.
Place a sheet of aluminum foil on a safe baking surface. The foil will allow for quicker clean up.
Cut the stems off the fresh green chilies. Salsa verde is traditionally a little spicy, but if this is a problem for you can remove half of the seeds or all of them according to your taste.
Prepare the onions by cutting off the root and top end, then halve into two large pieces.
Break a whole garlic bulb down to individual cloves. Leave the skins on as this will protect the cloves and allow them to get soft during the charring process.
Remove the papery husk from the tomatillos.
Leave the tomatoes whole and drizzle all of the ingredients with a small amount of olive or vegetable oil.
Once the broiler is up to temperature, place the ingredients in the oven and check often. The process of charring will happen quickly in most ovens (just under 10 minutes). Keep an eye on the oven.
Once the ingredients are well charred, remove from the oven and allow the items to cool, about 5 minutes. Remove most of the skins from the chilies and the garlic.
Set up a blender and add all of the ingredients. Process until all the ingredients are emulsified. Add a pinch of salt to suit your taste.