I'm back with another try, this time my friend made some "cake design" and I tried to follow your suggestions about lighting. I've used a flash (in an homemade lightbox) on the left and reflectors on the right. Here are the results:
giada01 di LucaSano, su Flickr
IMAGE LINK: http://www.flickr.com/photos/lucasano/12588972554/
016_100X: shooting with a flash di LucaSano, su Flickr
IMAGE LINK: http://www.flickr.com/photos/lucasano/12588648543/
giada02 di LucaSano, su Flickr
what do you think?