Cut the avocados in half, remove the pits, and scoop the flesh into a mixing bowl.
Mash the avocados with a fork until mostly smooth with a few small chunks remaining.
Add the lime juice, diced red onion, diced tomato, chopped cilantro, salt, and minced garlic to the bowl.
Stir everything together until the ingredients are evenly combined.
Spread the guacamole in an even layer on a serving plate.
Spoon the sour cream into a small zip-top bag, snip off one corner, and pipe four or five concentric circles on top of the guacamole.
Drag a toothpick from the center of the circles outward in straight lines to form the spiderweb pattern.
Set the plate on the table with a bowl of tortilla chips beside it.