Cleaning porcelain steel
Try dishwasher gel.

That burned on gunk is some sort of super grease.  If you get grease in an alkaline environment it turns to soap.  Ammonia works but it is stinky.  I used that on my barbecue grate - put them in a trash bag with ammonia and left it outside overnight.

Dishwasher gel works for that black gunk too.  The regular stuff like Cascade has sodium carbonate in it which is not quite lye but is very alkaline.  I used that to clean the burners on my gas stove.  I soaked them in the sink with some gel overnight and the stuff came right off.

Put some gel on each spot and leave it overnight.  Let me know in the comments if you can wipe them off in the morning.