Panna cotta is an Italian dessert which is simply softly set cream. It has the texture of a light mousse but made without the egg.
The chocolate sauce is simply melting a bar of unsweetened dark chocolate (I use Green & Black's organic dark chocolate) with some water and sugar.
I adapted Keiko's recipe which in turn is adapted from Delicious magazine (a food and drink mag in UK). This is a Jamie Oliver recipe who is a celebrity chef in UK.
Like Jamie Oliver said, "The best combo ever", which I totally agreed.
PS. Try to use matcha cooking powder instead of the much weaker drinking green tea powder or green tea teabag, the result is markedly different.