Remove the stems from 2 medium serrano chiles, slice them in half lengthwise, and place them in a large mixing bowl.

Remove the root from a small white onion, slice it in quarters and add it to the mixing bowl.

Place 2 cloves of unpeeled garlic into the mixing bowl.

Place the tomatillos into the mixing bowl.

Drizzle 1 tablespoon of safflower or corn oil over the vegetables and toss to coat.

Arrange the vegetables on the baking sheet in a single layer, and set the mixing bowl aside for later use.

Remove the leaves from 1 bunch of cilantro (enough for 1 cup of leaves).

Place the baking sheet in the oven directly under the broiler and broil for 4 or 5 minutes.

Rotate and shift the position of the baking sheet every so often to get even charring.

Different vegetables may roast at different rates. As vegetables develop an attractive char and start to soften, turn them over to roast the other side.

Continue to roast until the vegetables are cooked through. Remove the vegetables that are soft, and place them in the mixing bowl.

Once all of the vegetables are roasted, allow them to cool for about 15 minutes.

When the vegetables have cooled down enough to handle, remove the skins from the garlic and remove the tough outer layer off each onion wedge.

Place all of the vegetables into a blender or food processor and use a spatula to get all of the juices that have collected in the bowl or on the baking sheet.

Add the cilantro leaves.

Add a teaspoon of Kosher salt.

Blend everything to a coarse puree.

At this point, the sauce base can be placed in the refrigerator for up to 5 days.

Heat 2 tablespoons of vegetable oil, bacon fat or pork lard in a skillet or pot over medium-high heat (see note).

Once the pan is hot, but not smoking, pour in the sauce base and bring it to a simmer.

Let the sauce base reduce and concentrate, stirring frequently, for about 4 minutes.

Stir in 1 1/2 cups of chicken broth.

Turn the heat down to medium-low and let it simmer for about 5 minutes (or until you’re ready to use it.

If necessary, season the sauce with a little salt.