How to clean a trashed Circulon baking sheet

[marmaladegranny]

A long term house guest of DD & SIL repeatedly used their almost new Circulon baking sheet, probably using oil, in a high temperature oven and left it to cool before cleaning it. The result is a baking sheet covered with brownish slightly sticky residue.
I seem to remember reading somewhere that you could soak non-stick cookware in something like washing powder to get them back to nearly new. Can anyone endorse this or suggest another way of cleaning this tray?
Thanks in advance…….

You can soak in bio washing stuff and hot water, which may help. My mum used to do this and it's her top tip. However...

I like astonish paste (blue tub, £1 from most pound shops) and a scourer for crusty pans. It cleans them up like magic. I got a filthy range clean with it. I'm not sure if it's compatible with your tin. You'd need to check. But if it's ruined anyway...

Or you could try soaking in a very strong soda crystal solution. This may be your best starting point. As soda crystals are great for dissolving grease.

Thanks Bunny - we've tried the soda crystals but may not have had it strong enough so worth another try, or it's off to buy bio washing stuff!

Oven Pride? Put the baking sheet in the bag with the solution. I used it on a completely manky grill pan (years of baked on muck): came out like new. It wasn't me who hadn't been cleaning the grill pan btw....