Heat a large dry skillet over medium-high heat for 2 minutes until hot. Place the tomatoes, onion wedges, and garlic cloves in the skillet. Cook, turning occasionally with tongs, until the skins are charred in spots and the vegetables are softened—about 8-10 minutes for tomatoes, 6-8 minutes for onion and garlic.

While the vegetables char, toast the dried chiles in a separate small dry skillet over medium heat for 30-60 seconds per side, until fragrant and slightly puffed. Do not let them burn—they turn bitter instantly. Transfer to a bowl and cover with hot water; let soak for 5 minutes. Drain.

Transfer the charred tomatoes, onion, and garlic to a blender or food processor. Add the soaked chiles, salt, cumin, and 1/4 cup of the water. Pulse until the salsa reaches your desired consistency—I prefer a slightly chunky texture with small visible pieces of tomato and onion. For a smoother salsa, blend continuously for 30 seconds.

Pour the mixture back into the same skillet (no need to wash it—the residual char adds flavor). Place over medium heat and bring to a simmer. Cook, stirring occasionally, for 5 minutes. The salsa will darken slightly and the flavors will meld. If it seems too thick, add the remaining 1/4 cup water, 1 tablespoon at a time, until it's a spoonable consistency.

Remove from heat. Stir in the lime juice and cilantro, if using. Taste and adjust salt. Let cool for 5 minutes before serving warm, or refrigerate to serve cold. The salsa will thicken as it cools.