Much like Granny C's enchilada sauce, we mix to taste.
Start out with a large bowl food processor and your tomatoes. Pour in the can, including liquid. You could also do 1/2 fresh, 1/2 canned but the texture ends up a bit grainy when you cant find ripe tomatoes.
add 1/4 of the onion, your garlic, and cilantro. cut just the top off of one jalapeño at a time (dont de-seed) and toss it in, processing until almost smooth. depending on how hot your peppers are, use up to 3 of them. dont forget to taste after each pepper!
Add more onion, garlic, cilantro to taste.
If you want this like grandmas, add 1 dried red chili and a generous dose of salt.
I generally do a 2 jalapeño, 1 serrano ratio and that's hot enough for me.
If your crazy, use one of each kind including a habanero and feel your face melt!
If you want it sweet and spicy, use a few Anaheim peppers with the jalapeños.
This freezes well and doesnt seem to affect the heat:)