Doña Martha begins by snapping the stems off each chile de arbol -- the little red hot devils. 

Then she adds one quarter of a large white onion, 6 tomatillos, a clove of garlic, salt, water to cover and simmers until everything is softened.

She sets a tomato over the fire to toast and turns it until it is well blackened.

Meanwhile, she moves the chile mixture to the blender.

When the tomato is well toasted, she removes the skin and adds the tomato to the blender.

When the salsa is well puréed, chopped cilantro is added and blended very briefly -- just a couple of quick pulses.

Sometimes she makes this salsa using jalapeno or serrano chiles.