I have also tried the more fascinating rigatoni con la pajata.
Back in the old days, the quarter I'm staying in, Testaccio, was the slaughterhouse district. The workers would get the leftover scraps, offal, etc., called the fifth quarter (quinto quarto), and would have to figure out some way to make it edible. So this dish is true testaccina cuisine.
Not for the squeamish:
Pajata are intestines, but specifically the intestines of unweaned calves (so they only eat milk). The intestines are cleaned and skinned, but the milk is left inside, so when they're cooked, the milk turns into a cheese, kind of like ricotta.
You can apparently find pajata in some places grilled, but it is (more?) commonly served with rigatoni in a tomato sauce. My theory is that it's because they are the same circumference as rigatoni, so if you cut them into two-inch sections, they blend right in. Lovely.