Melt the unsalted butter on a low heat for 5 minutes or until it becomes brown butter and turn off the heat.
Add the white chocolate powder and stir until dissolved.
Put the ice cubes into the mixture and stir until melted, then set aside for later.
In a large bowl, whisk together the eggs, vanilla paste and sugar until it becomes fluffy.
Sift in the matcha powder, white chocolate powder and salt into the egg mixture, then fold in until well incorporated.
Pour in the brown butter and mix well.
Melt 225 g (8 oz) of the green tea chocolate in a heatproof bowl over a pot of simmering water on low heat, then add the melted chocolate into the batter and stir to combine.
Sift in the flour and fold in until mixed.
Roughly chop the remaining green tea chocolate bars and stir into the batter.
Line a 23 x 33 cm (9 x 13”) with baking paper, then smooth the batter out until it covers the entire tray.
Roughly chop all the white chocolate, then top it over the uncooked batter.
Cover the uncooked brownies with glad wrap and refrigerate for 3 days.