It's being reabsorbed as soon as you pull it off.
“I can see that. The question is, what to do about it?” Dill thought back to Harold's mum's house, the night they collected the treatise. “When Ada made the spider homunculus, Harold was able to pull bits off it without them being restored, but it grew them back again. Perhaps if I get someone else to pull bits off it'll expose the sigils.”
Maybe, but who? All you've got in the house are the ghosts and the kid. Who are you going to ask? It's not like you can walk down the street, is it?
“There's the imp...”
Who probably did this to you in the first place, since it was them that made the body.
“Oh.” Dill frowned. “What if I used a tool to carve my head away? Do you think that would work? If I wasn't actually in contact with the dough I might be able to scrape it away.”
Sounds reasonable. Where will you get the tool? Is there a garden shed?
“I can try the kitchen. There's bound to be something in there.”
Maybe. Just be careful of the oven, given what you're made of. We don't want to be the Gingerbread Man, do we?