I am not an expert on this, but the creamy version has avocado in it. I have made it and it was decent, but not as good as some of the others that I have had. Here is what I would try.
-Boil a few jalapeno's or serranos with some onion and a whole garlic clove or two. You might try and saute them briefly first in some olive oil, I mean just for like one minute or so and then boil.
-Take that out and liquify in a blender or mush the hell out it in a molcajete.
-Then get two, maybe three, avacados(make sure they are just ripe or a little bit towards being ripe.
-Add some cilantro, not too much as you don't want it overpowering the salsa. I like cilantro, hell I grew up in Mexico, but too much of it is not a good thing.
-Blend all that stuff together, liquify. Maybe add a dab or two, maybe a little more of Mexican cream, not sour cream, but the mexican style cream you can buy. Put that in to your taste.
-Add salt to taste.
-I would reserve some of the jalapeno/serrano mush and add it if you want it spicier.