Not baking, but I was making jelly to bring to a Thanksgiving market. On the last batch I made a rookie mistake - I stepped away from the stove to put a bowl in the dishwasher. DO NOT EVER leave a pan of jelly unattended - even for the time it takes you to move 6ft away (and back)! Wish I could attach a photo of what my glass-top stove looked like afterwards. It was too gooey to scrape entirely off so I had to turn both front and back burners on High and burn it off. The house smelled like caramel, but the jelly was good - one of the best I've ever made (of course I had to sample what was left in the pan after filling 8 jars). Ouch on the Thermopen - but I made a similar (not quite as expensive!) mistake when I was a new mom. I had bought some snap-block (puffy plastic) links for my son at a consignment store. Of course I had to wash them but water got inside and I didn't want them to mold, so I put them in an oven I'd warmed to 170 degrees then turned off. All was fine until, just like you, I wanted to bake something and turned it on to preheat...

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