line inside of parabolic dish with heavy duty foil (smooth out the wrinkles), shiny side up, or btter yet, epoxy small squares of mirror, making a solar cooker =o)
Careful where you casually leave it outside, so you don’t accidentally burn down the barn.
...that is all
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There was a Bonanza TV episode about this. Mickelson and his speed of light experiment.
EXCELLENT memory right there!