Leave the cream and butter at room temperature for about an hour. Put the chocolate and heavy cream in a heatproof bowl and place over a water bath. Keep mixing until all the chocolate has melted.
Add the previously sieved matcha powder to the mixture bit by bit, constantly stirring with a whisk until you get a homogenous mixture without lumps. If the mixture becomes too thick, place it back on the water bath and continue stirring.
Heat the oven to 160 C.
Whisk together the eggs and add the sugar, mix to incorporate. Add the egg mixture to the white chocolate.
Meanwhile heat the butter in pot on medium low heat until butter has totally melted. Add melted butter to the matcha white chocolate mixture.
Pour the mixture in a baking form lined with baking paper (bottom and sides). Place the form in bigger oven form, then pour boiling water in it.
Place in the preheated oven and bake for 40 minutes.
Take out the fudge and let it cool. Then place it in the fridge overnight. Take your fudge out and cut in squares or whatever shapes you prefer :)