Pre-heat the oven to 170 degrees C. In a bowl, add the green tea leaves to flour. In a mixer, cream sugar and butter then add half of the flour and 1 egg – beat until smooth. Add remainder of the flour and other egg – beat until smooth. Finally, add the milk and mix through. Pour your green tea mix into a greased, lined baking tray. Bake at 170 degrees C for 15 minutes, use a cake tester or skewer to see if it's done. When its ready, remove the tray from the oven and set aside to cool on a cooling rack. Once it's cooled properly, cut it into squares and set aside for later.
In a medium pot, heat up the cream and milk. While the cream and milk heat up, add the sugar to egg yolks and whisk until pale then pour the warm milk and cream mix steadily into yolks and return to a medium heat, stirring continuously until the mixture coats back of a spoon then remove it from heat. Pass the mixture through a sieve and into a bowl, chill until needed.
To Finish: Make sweet croutons by cutting the cake into 2cmx2cm cubes then toast in a 180 degree C oven for about 10 minutes. Blend the dry ice into a powder – using a blender and pour the chilled ice cream custard into a mixer. With a whisk attachment, mix the ice cream mix on a medium speed, spooning in the dry ice powder. Increase the mixing speed as the ice cream begins to set. Serve the ice cream on top of the cubed green tea sponge. Serve immediately.