Very :-). I'm talking about a pan accidentally left on the grill or in the oven for too long until it smokes. The residue is pretty much what you end up with when seasoning cast iron cookware, and is very hard and resistant to usual household chemicals. It's far from the oily residue that is removed easily with paint thinner or acetone.
Oven cleaner (Easy-Off heavy duty or similar), in a sealed plastic bag with the item in question, left for 24-48 hours. Rinse thoroughly with tap water, then DI water, then distilled vinegar, then tap water & DI water again. Works to strip cast iron, should work for similar gunk. Obviously wear appropriate PPE (long rubber gloves, follow all warnings on the oven cleaner, work in a well-ventilated area, the MSDS[1] is useful though all instructions should be on the label).
If the cookware is metal you can use electrolysis.
Car battery charger clamped with an electrode to sacrificial metal plate and an electrode to cookware; both hanging apart from each other in a bath of electrolyte made of water + sodium carbonate. Let it work for a day or so in a well ventilated area (it will create hydrogen gas).
Have you tried barkeeper's friend with a nylon scrubbie or steel wool? I've found that to be excellent, if labor-intensive, at returning stainless steel to like-new condition, even when dealing with oily residue that's been baked at 500 degrees.
Very :-). I'm talking about a pan accidentally left on the grill or in the oven for too long until it smokes. The residue is pretty much what you end up with when seasoning cast iron cookware, and is very hard and resistant to usual household chemicals. It's far from the oily residue that is removed easily with paint thinner or acetone.