Dice the avocados (I do this with the avocado still in the peel after halving and carefully removing the pit). In a bowl, combine the avocado, sour cream, lime juice, onion, garlic, and salt. Mash with a fork to achieve a fairly smooth consistency. I like to leave some larger pieces of avocado for texture.
Gently fold in the tomatoes. Taste, and add as much salt as you'd like to the dish - remember that avocados generally need a good amount of salt to balance the tart of the sour cream and lime. I generally use close to 1 teaspoon total of kosher salt, depending on the size of the avocados.
Serve with chips immediately. Enjoy!
Notes
I use a microplane to grate the garlic and onion to catch all the juice in the dip. If you don't have a little grater just finely chop/mince the onion and garlic together.
If you'd like to prep this, just prep everything but the avocado in a bowl, then mash and stir in the avocado and tomato at the last minute to prevent it from turning brown.
OPTIONAL: I have made this with ½ teaspoon of ground cumin before, and love this variation. Add a sprinkle of cumin if you'd like a deeper smoky flavor, or leave it out for a brighter fresh flavor.