Place the halved tomatillos and the whole garlic clove in the large skillet lined with foil. Set the skillet over medium heat and and dry roast for about 3 to 4 minutes per side. The tomatillos should be soft and blotchy and the garlic will be browned.
Transfer the roasted tomatillos and garlic to the blender. Add the jalapenos and cilantro. Blend until you have a smooth consistency. Pour into a serving bowl.
Rinse the chopped onion and stir into the salsa. Add salt to taste and serve.