https://www.sciencenews.org/archive/curly-cooker
This article is paywalled, but I've had a photocopy of this magazine cover since the 1980s that just srted to the top of a stack.. The article is paywalled, but everything you need to know is in the cover illustration.
Invented by a high-school student but it never went anywhere (that I'm aware of). So, if you grasp the inner an outer ends of the spiral and twist the spiral springs into a 3D shape. It acts as a 'Fresnel lens'.
At shallow angles it concentrates at a center above the spiral. At steeper angles it focuses behind the spiral.
In a post-apocalyptic scenario this could be valuable information.