Kettles, mash tuns, infants, etc
If it's on stainless steel Bar Keepers Friend will clean off just about anything. I use this on my ss pots and pans and it works great (I try not to use it on mirror finished surfaces though).
You can find it at Bed Bath & Beyond, Walmart, the grocery store, just about anywhere.
EDIT: I also believe that Bar Keepers Friend is a glass cooktop cleaner, so it can def cut through some scorched on food/sauce/liquid.
It's toxic as heck, but standard oven cleaner is your last stop. My progression would be:
I think an angle grinder with an abrasive pad will do the trick. That method is somewhere between Barkeeper's Friend and oven cleaner.
I use PBW (Powdered Brewery Wash) and that gets everything off that I've ever used it for including scorching.
Try vinegar and baking soda. It works for pots and pans.
I'd try using the PBW as a scouring agent itself. Soak the pot with warm PBW for twenty minutes. Empty the kettle. Sprikle in some fresh PBW without adding additional water, and scrub with a green pad.