Bar keeper friend and magic eraser.
A product such as powdery " Comet" should do the trick. Put some on a wet sponge ad go to work.
Hi Victoria, this may help,
I use soft scrub and a scrubby.
Hi Victoria: You can try Krud Kutter or a non-caustic oven cleaner. I have heard good things about Kohler Cast Iron Sink Cleaner. It looks like Soft Scrub but it's a different formulation. It takes a lot of rubbing but if you do a bit at a time it is manageable. Good luck