I made Toad in the Hole this evening, and absent-mindedly used self raising flour instead of plain.
It didn't dome up with those deliciously crispy, puffed-up-and-curled-over edges. It barely rose at all. 
It turned into a squidgy, doughy, savoury 'cake', utterly delicious with gravy and greens.
Out of the disaster of thinking I'd ruined the dcs' favourite supper, I hear "Make this again, Mum!"
What have you accidentally invented?