The basket occasionally went in the dishwasher which cleaned the surface, but the well gunked grease has been building up.
Tried soaking the basket in soap and hot water. Scrubbing with a soft sponge. And then running the dishwasher multiple times but it only got a small part of the grease out.
Silly suggestion, and no idea if it will work, but it’s an easy one to test;
Get some cooking/vegetable oil, and see if it will help dissolve the residue by putting a bit on some kitchen towel and either scrubbing with the oiled paper towel or leaving that towel on the residue for 10 mins and seeing if the grease has softened.
If the oil does seem to dissolve/soften the grease residue then you can add some bicarb/salt to act as gentle abrasive as it won’t dissolve in the oil as it would do in water
I’ve used cooking oil to dissolve tar/bitumen paint from my skin and clothes before and you can then use soap to clear the dissolved tar in oil.
Otherwise use a kitchen degreaser like you’d clean a traditional oven with.
I imagine what’s happening with the oil is something akin to polymerization, so you either need to break the polymers bonds or dissolve in a suitable solvent
Not silly, that’s a common cleaning technique from janitor/cleaning staff i was told a while back. Use a little bit of what causes the stain/gunk and it helps break down the bonds by binding with the already-solidified object and trying to mix with it, weakening/changing the concentration of the ‘stuck’ substance