I make steel cut oats in the pressure cooker; you need to put some fat in there to stop it bubbling while it's cooking, so butter has a physical purpose there too. And also tastes delicious.
Some proteins seem to have a similar effect - but I haven't tried to narrow that down, and don't know the food science behind it.
Also, (and I learnt this much too late in my life), cook the pasta until a few minutes before it's done, and _finish cooking in the sauce_. This is what makes the sauce adhere. Keep a cup of the starchy pasta water to add in case it needs to be loosened a bit.