In a casserole, preferably made of terracotta or enameled cast iron, gently sauté the onion, carrot and celery in abundant olive oil until the vegetables have softened.
Add the lentils and mix. Let it all simmer gently for a few minutes, then add a splash of the wine and let it evaporate.
Add the passata and water, along with the bay leaf if using. Simmer gently, uncovered, for a good hour or more, until the lentils are fully tender but not falling apart. Add more water as needed to keep the lentils just barely covered with liquid.
Perhaps 15 minutes or so before the lentils are done, season to taste with salt and pepper. Adjust also for liquid. Your lentil ragù should be thick but pourable, just as a meat-based ragù would be.