OP this makes me feel much better. I too have a tale of cooking pot woe that nearly cost us a lot of money...
Last summer I noticed a smell in the small room/larder area off the kitchen - it's a long thun room that goes under the stairs (we live in a terrace with the kitchen in the converted basement). It is quite an old house and I initally thought it might be damp - a cursory look in the larder walls and floor didn't seem to indicate damp, however I resolved to call someone about it when we got back from a week away.
Coming home after holiday and opening the front door, the whole house smelt like dead cabbage. It was a horrible, fusty-farty smell which no amount of airing seemed to shift and it was definitely coming from the larder area. Further sniffing established that it was stronger near the ceiling and weaker nearer the floor which lead us to the conclusion that we must have something dead in the basement ceiling space near the stairs.
Apart from the fact that I was horrified we might have mice or rats, I also thought we'd have to take down the ceiling at least part way in the basement to remove offending creature and establish how the fuck it got in.
So, I spent all morning dutifully emptying the vast majority of the larder room, then went to put on a casserole for tea.... and voila! Source of smell identified!!
However the word smell doesn't even come close to the pungent, fetid, stench that leapt out of the putrified liquid in the casserole dish and assulted my senses.
It violated all the airspaces in my head and burned my eyes.
In fact it felt like it was actually melting the very flesh off my face in those milliseconds before I slammed the lid back down - sort of like that bit from Indiana Jones and the Temple of Doom, except I'm not a Nazi and had not done anything to deserve such a fate.
I ran out the room, took a few gulps of fresh air, then went back in, grabbed the dish, ran back outside with it and put it on the garden chair. Last time I could recall making anything with that dish was ONE MONTH before we went on holiday which meant it has festered for a total of 6 weeks. IN SUMMER.
There was not enough bleach in the world for me to touch it again. So I panicked and did what any sensible person would do and put gaffer tape all over it and stick it in the bin.
I was torn between being completely disgusted, amused and/or relieved. I was ready to start poking holes in the ceiling and forking out for pest control and builders to reattch the ceiling!!! Thank fuck I found it beforehand.
Picture is what I sent to DH at work the day I found it. He found it all hilarious. He didn't have to smell the raw horror in that dish. Our replacement dish it cream as I couldn't bear getting another red one!