Mexican salsas are not one thing — they're an entire family of preparations ranging from raw (salsa cruda/pico de gallo), to charred (salsa tatemada), to cooked (salsa roja cocida), to dried chile-based (salsa de chile de árbol), to creamy (salsa de aguacate). Each uses different chillies, different preparation techniques, and serves a different purpose at the table. A proper Mexican meal might include two or three salsas, each providing a different flavour and heat profile. The molcajete (volcanic stone mortar) produces a fundamentally different texture than a blender — rougher, more integrated, with the stone's seasoning contributing subtle flavour.
Salsa cruda: raw tomato, white onion, serrano or jalapeño, cilantro, lime juice, salt. Diced by hand — never blended. The texture should be chunky with visible distinct ingredients. Salsa tatemada: tomatoes, chillies, onion, and garlic charred on a comal or directly over flame until blackened, then crushed in a molcajete or roughly blended. The char IS the flavour — don't remove it. Salsa verde: tomatillos (not green tomatoes) roasted or boiled, blended with serrano, garlic, onion, cilantro. Should be bright, tangy, and green. Salsa de chile de árbol: dried árbol chillies toasted and blended with garlic and salt — thin, fiery, and smoky. Each salsa has a specific consistency and heat level that matches specific foods.
The simplest salsa that every Mexican kitchen has: salsa molcajeteada — charred tomatoes, charred serrano, garlic, salt, crushed in a molcajete. Takes 10 minutes and transforms any meal. For salsa verde cruda: raw tomatillos, serrano, garlic, cilantro, onion, blended — this bright, raw, tangy salsa is what goes on tacos de carnitas and chilaquiles. The heat should be present but not dominating. Always taste and adjust — a salsa should hit salty, sour (lime), spicy, and fresh (cilantro) all at once.
Using a blender for salsa cruda — it should be hand-cut. Removing the char from tatemada salsas — the blackened bits are essential. Using green tomatoes instead of tomatillos for salsa verde — completely different fruit. Over-blending any salsa to smooth purée — Mexican salsas should have texture. Under-salting. Using dried chillies without toasting them first. Substituting canned tomatoes for fresh — the texture and flavour are fundamentally different.