Place tomatoes, tomatillos, garlic, and jalapenos in a saucepan, and add enough water to cover. Bring to a boil, and cook for 15 minutes, or until vegetables are tender.
Remove from heat, drain, and allow to cool.
Place avocados, the cooked vegetables, sour cream, and cilantro in a blender or food processor, and blend until smooth. Season to taste with salt. Cover, and refrigerate until ready to serve.
