Back in the day when I first made Salsa Verde, I boiled the tomatillos, onions, jalapeños, and the garlic. Though the flavors were nice, they just weren't bold like I wanted. But since I was very new at making it I didn't know any different. After years of making it, in all different ways, I think roasting the ingredients is the way to go. I start out by preheating my oven to 450* and putting the shelf in the middle. I then line my baking sheet with foil, this helps with transferring the ingredients to the bowl or jar. Next I coat the, already washed, tomatillos, onions, garlic, and jalapeños with olive oil and kosher salt, and place them on the lined baking sheet. I place in the oven for 30 minutes. They will cook down quite a bit and the juices will fill the bottom of the baking sheet - this is ok, just be careful when taking it out of the oven. After 30 minutes they should be nice and brown on the tops of the onions, jalapeños, and the tomatillos. Gently stir and put back in the oven. Cook for about 5-10 more minutes and then Turn off the oven - but leave the pan in the oven for about 20 minutes with the oven off. This will help with the carmenlization. Remove from oven, let cool for about 15-20 minutes. Spoon or dump the roasted goodness into a bowl or blender jar, making sure to carefully scrape down the sides of the foil - where all the carmenlization is. Add the rest of the ingredients and blend until smooth.
If using for salsa - refrigerate for a couple of hours until its cool and then serve.