Source: Food52, August 22, 2013

Makes 1 to 1 1/2 cups

small head of garlic
3 or 4 roma tomatoes
1 or 2 heirloom variety tomatoes (Box Car Willies or Wisconsin 55 are good)
poblano pepper or 3 jalapeños or your choice
3 to 4 half-inch-thick slices of red onion, left intact
Kosher salt and freshly ground pepper
Handful of cilantro
Splash of red wine vinegar
Drizzle of olive oil
Fire up your charcoal grill. Let the coals get blazing hot. 
Wash the vegetables.
Place the garlic off to the side of the coals where it will brown the paper skins but not burn the cloves. The garlic will take the longest to cook of everything. Let it get good and brown on all sides.
Now place the tomatoes and peppers right on the coals. Let them blister and blacken. Remove them to a tray. Let the juices collect in the tray.
Place the grill grate on the grill and grill the onions until they are caramelized and soft.
If you plan to grill more stuff, like a nice skirt steak, you will probably need to add a few more coals to the fire. You be the judge.
Peel the pepper, being carful not to spill or lose any pepper juices. I remove the seeds and, obviously, the stems. Put peeled peppers, tomatoes, onion, and peeled roasted garlic cloves into the bowl of a food processor. Add the tomato and pepper juices that collected in the bottom of the tray.
Add a two-finger pinch of salt, some pepper, half the cilantro, the red wine vinegar, and olive oil. Pulse the processor until the salsa reaches your desired consistency. I like this particular salsa smoother than most but still chunky. Taste the salsa and adjust the seasoning as necessary.
Pour into a serving bowl, garnish with cilantro, and serve.