A great guac starts with great ingredients
Sometimes, the simplest is the best. Which explains why traditional Mexican guacamole has only a few ingredients: avocados, chilli peppers, tomatoes, white onions, and salt. These days, many guac recipes add lime, coriander, cayenne pepper, yogurt, basil, and jalapeno, amongst other ingredients. Whether the addition of these ingredients makes a guac yummier is a pure personal choice.
Here's a short checklist of what you'll need.
Avocados - The key ingredient in all guac recipes. The Hass avocado is the darling of the bunch and the preferred product for making guacamole
Chillies - The serrano chilli (along with the jalapeno) is the most common chilli in Mexico so it stands to resaon it would be the first choice for your guac. This small slender chilli can be quite hot, so chop it finely before adding to your guacamole.
Onions - In Mexico, the most commonly used onion is the white onion. Unlike the yellow, red or purple onion, the white onion is not sweet and has a pure hot flavour. Chop the onion to a fine, even size for use in your guacamole. This will allow the flavour to blend with the avocado, but not overpower it.
Tomatoes - Select ripe but still firm red tomatoes. If tomatoes are not in season, you may want to purchase Italian or plum style for the most flavour.
Coriander - The leaves (and stems) of the coriander plant. Coriander has a very pungent odour and is widely used in Mexican cooking. Coriander leaves look a bit like flat Italian parsley and are related. Make sure to select crisp looking leaves for the best results.