In a molcajete, add the white onion, cilantro, and serrano chile. Grind the ingredients together until they form a paste so that the juices mix.
Hint: The molcajete is a mortar and pestle made from black volcanic rock and is used in mexico to make guacamole. If you don’t have a molcajete, use a large heavy bowl and a wooden spoon to grind the ingredients.
Halve the avocados, discard the pits, and scoop out the avocado in large chunks with a spoon. Gently mix with the onion paste in the mocajete, mashing the avocado slightly.
Gently mix in the diced tomatoes, lime juice and salt. If needed add extra salt and serrano chile to taste.
Hint: Avocados brown quicker if not diced into cubes before mashing. The lime juice also helps to preserve it’s color. The browned avocado doesn’t taste any different, it just looses it’s appeal. So make it just before you’re ready to serve it! Enjoy!