Montezuma and his predecessors were said to have enjoyed ahucamolli, or avocado sauce, as a dish prepared with mashed tomatoes and onions in their courts. Adding lime certainly helps to keep the fruit from browning, but neither citrus nor cilantro made it to Mesoamerica until the 16th century. Use room-temperature avocados when you can; their delicate flavor can be numbed out when served cold.
4avocadosripe and at room temperature
1small white onionfinely diced
1tspsaltor more to taste
Slice the serrano chile in half lengthwise and remove seeds if you’re afraid of too much heat. Finely dice the chile or pound with a molcajete (or mortar and pestle).
Pick the leaves from the stems of your cilantro. Mash the avocado in with the chile and fold in the cilantro, onion, salt and lime. Taste and adjust seasoning.