How to fix separating spaghetti sauce? I am making spaghetti sauce from home-grown tomatoes. They were standard garden tomatoes - not Romas or anything you'd traditionally use for sauce, but hey, they're what I had.

The sauce has been simmering for a few hours and is reducing nicely. To stir, it has a lovely consistency, but when it sits, water collects at the bottom and the sauce becomes almost mealy until I stir it all up again.

In other words, it's not just thin and "watery," but the liquid (virtually clear by itself) is actually separating out.

The sauce doesn't necessarily need to be "thickened" (although it could be), but I'd like to stop it from separating like this. I'd rather avoid using canned tomato paste if possible. Any other ideas?
Par-blending the sauce (eg with a stick blender) could thicken/emulsify it just enough to stop it from separating but without adding any thickener.