I use old electric hob (as shown in the picture) for preparing my food, which takes a while to heat up and then takes even more time to cool down after use. Today I made a grave rookie mistake - as the hob was cooling down, I thought it would be a good idea to put my plastic cup of water on it, in order to warm it up. One minute later I recognized that the plastic began to liquify due to heat still being there, apparently...

Now, the second biggest mistake probably was my reaction, as I hurried to scrape the remains of hot plastic with a knife, which removed 99% of it, but a small visible layer of it still remains. It probably was not an issue, if the metal surface was smooth - but it's actually composed of many little notches, which makes it somewhat difficult to reach and clean them.

Therefore my question is - how do I remove that plastic layer lurking on top of the notched metal surface? Will heating itself be enough for it to slowly evaporate, or is there some other 'smart' way to react with this plastic?