Step 1Set up a charcoal grill for direct heat or heat a gas grill to medium. Alternatively, heat a large skillet or grill pan over medium-high heat.
Step 2Arrange the tomatillos and jalapeños on the grill in a single layer and cook, turning to evenly blacken, until tender and charred, about 20 minutes.
Step 3Transfer the tomatillos to a blender and the jalapeños to a cutting board. Cut the stems off the jalapeños and discard; cut out the seeds and ribs and reserve. Add the jalapeños’ flesh to the blender, along with the cumin, mushroom powder, lemon juice, and 1 teaspoon salt. Blend until slightly chunky yet smooth. Taste and add more salt if needed and the reserved jalapeño seeds and ribs if you want a hotter salsa. Add the cilantro and blend, leaving small pieces of cilantro.