Peel the heirlooms with a sharp knife. It doesn't have to be perfect - this is intended to be a rustic tomato sauce. Core the tomatoes and chop them into 2 inch chunks. Place in a small pot over medium heat.
Add the Balsamic Roasted Tomato halves. (I keep this staple in my refrigerator all the time. It's amazing the number of uses I find for them.)
Add the olive oil, and a pinch each of salt and pepper and stir.
Simmer until the sauce reaches the thickness you prefer. I typically simmer mine for about 30 minutes, but this at least partly depends on how juicy the heirlooms are that I'm using. Correct for seasoning.
I've refrigerated mine for up to two weeks without any problem.