Place 1/2 jalapeño, cut into chunks and 1/2 yellow onion, cut into chunks into food processor. Process it for a few seconds.
Add 15 ounce can tomatoes and green chiles, 15 ounce can whole peeled tomatoes, do not drain, 1 teaspoon garlic salt, 1 teaspoon kosher salt, 1/2 teaspoon ground cumin and 1/4 teaspoon sugar and process all ingredients for just a few more seconds, keeping it slightly chunky (not a puree).
Put into a bowl with a lid (I like to use a large mason jar) and chill in the fridge for AT LEAST SEVERAL HOURS (overnight is even better).
Then serve with tortilla chips.
Video
Notes
Please do not eat right away. YOU MUST let this marinate for several hours (overnight is best.) Trust me, this makes a HUGE difference.
Add fresh cilantro if you enjoy the taste.
A blender can be used in place of a food processor.
For less heat, remove the veins/pith and seeds from the jalapeño after slicing.
You don't taste the sugar, it just helps cut some of the strong acidity from the tomatoes.