passata is just skinless, seedless tomato puree.
1. cut an "x" in the bottom of a bunch of roma tomatoes
2. boil tomatoes for 30 seconds or so
3. take tomatoes out and dunk them in water (most recommend ice water, but it's not necessary)
4. pull skins off
5. halve and push seeds out
6. blend or push through strainer
actually, the pulp has a lot of flavor so i don't bother pushing the seeds/pulp out. if the seeds really bother you, you can strain the puree.
this will produce a sauce that's much lighter and thinner than the sauce you get from canned tomatoes. i could never figure out why that was, but i think i finally learned: after simmering the passata for a long time, it thins, darkens, and looks a lot like the store bought stuff (e.g. pomi brand:
http://www.pomi.us.com/StrainedTomatoes.php). i think the professional canneries must either cook their tomatoes or remove the moisture some other way.
