Solar Cooking

I intend to make a solar cooker. This is how far I have got:
Peak power 600 watts per square meter. So the trick is to focus the rays from one square meter at a small target volume.
If you did focus 100cm x 100cm into the small volume:

1 watt = 1g water by 1 deg C in 1 sec

200 watt = 200g water by 1 deg C in 1 sec

600 watts = 200g water by 60 deg in 60 sec

Is the maximum you could get - but that ain't bad.

Here is a cardboard box design : http://www.freewebs.com/sunnycooker/suntasticcookerplan.htm