Add the cilantro, parsley, serrano pepper (if using), shallot, and garlic to a food processor or blender.

Pulse a few times to finely chop the herbs and aromatics.

Add lemon juice, cayenne powder, smoked paprika, cumin, salt, and saffron (if using). Pulse again to combine.

With the processor running, slowly drizzle in the olive oil until the sauce reaches your desired consistency.

Taste and adjust seasoning, lemon, or oil as needed.

Use immediately as a marinade or sauce, or refrigerate to allow the flavors to meld.