Turn the oven broiler on high, with the rack set near the top (one notch down from the very top slot).

Add the husked and rinsed tomatillos, onion, jalapeños, and garlic cloves (skin still on) to a foil-lined baking tray.

Broil for about 4 minutes, until the tomatillos develop a nice bit of char.

Flip the tomatillos and broil for another 4 to 5 minutes, until charred on the other side too.

Once everything is nicely charred, peel the garlic cloves out of their skins (they should be roasted, not burnt). Add the garlic and all the roasted vegetables to a blender along with the cilantro, lime juice, bouillon powder, salt, and cumin.

Pulse until you get a nice uniform salsa — don't overdo it, this shouldn't be a purée. You want some texture left.

Heat a skillet with 1 to 2 tablespoons vegetable oil over medium-high heat.

Pour the salsa into the hot skillet and flash-fry/simmer for 3 to 5 minutes, stirring constantly, until slightly thickened. This concentrates the flavor, mellows the tomatillos' tartness, and helps the salsa keep longer.

Pour the salsa into a clean container to cool. Let it cool to almost room temperature before putting the lid on so steam doesn't get trapped inside.