1/3jalapeno, finely chopped (with or without seeds)
In a large bowl, add the avocados, diced onion, fresh cilantro, lime juice, salt, and jalapeno. (Add the jalapeno seeds for extra spicy guacamole, or leave them out for a more mild flavor.)
Use a fork to mash everything together until relatively smooth. Taste and adjust the seasoning as needed. I usually add an 1/8 teaspoon more salt, but that varies depending on the size of the avocados I use each time.
Serve right away, or store in an airtight container in the fridge for up to 48 hours. (See storage tips in the post above.)