I am trying to cook using solar energy only. My prototype is a cardboard shell lined with aluminum. I am certain polished mirrors would reflect more energy to the cooking area than foil. But, my project is very cheap to build. Forecast is cloudy and a little cooler. Where are the 110 degree sunny days when you need them, eh?
If I could experiment a little, then I might be able to refine things. Best heat I could get, and I was only "cooking" water yesterday, was 127 degrees. That's not really hot enough to kill food borne bacteria let alone cook actual food. Still, the concept is working. The food area was much hotter than the 99 degree temperature in the surrounding area.