Silly is hard. There are several blog posts that talk about the D&D world as being the straight man to the party, rather than the other way around. A more sinister vibe would get around it being thought of as silly. Not over the top, I think you are already pretty close to where you need to be.
Golem Room:
What's the point of the hot spring? It feels tacked on. How could it contribute to the adventure? It should also be higher up in the description, before the golem, since its likely to be the first thing seen/experienced AND its short. Good golem stuff, but the ring in the middle seems a little too hidden. Some hint elsewhere, that makes the party want to kill their friend to get the thing that will help them defeat the witch? Then it's a Delicious choice!
Cauldron Room:
This feels like an Ed Greenwood room. Just something to see and not really interactive. What if the candy was real, living candy people? Or there was some way to use the liquid candy to do something, like make your own candy people?
Oven, supplies:
How is this interactive/how does it drive interactive play and/or contribute to the adventure? Not that everything has to, mind you, but this IS a short adventure. Same for those treacherous caves in the NE. DId you mean for the DM to insert some challenges? Maybe more specificity/different word choice would drive that?
Catacombs:
Footprints relate to the chittering? I immediately thought "track something in another room!" rather than "hint about the rats." Mostly because tracking is interactive and a hint about rats, that dont appear, seems window dressing. Would be nice if the fruit trees on the door meant something.
The witch is good but Jasper is missing something. It feels like the encounter is off, like Jasper needs one more bit of information. I think I get where you are going, but I can't put my finger on whats wrong. He wants kids and hates the witch and the golem, in different ways ... but that's not it. Maybe he is unredeemingly evil, with nothing to offer? The witch will pay, but Jasper seems like he's just a jerk ... and he wants to eat kids and fuck up that golem? What's he got to offer? There's not pretext that a party can use to ally with him? I'm not sure thats accurate,.