Wappa - a traditional japanese craftwork. they bend thin slices of cedar in round shape and staple the edges by small pieces of cherry bark. because it is made of wood, it keeps moisture in rice in the best balance, as well as keeping food from decay.
I love carbonara and I'm always fascinated by new takes on what is a very simple recipe. I tried something like this at a restaurant in Brittany many years ago and the egg yolk concept was delicious. Must try it again one day.