1 Brush a 9-by-13-inch baking dish with butter.
2 In a large pot, melt the 5 tablespoons of butter over moderate heat. Add the marshmallows and cook, stirring with a wooden spoon, until completely melted, about 3 minutes.
3 Remove the pot from the heat, add the cereal and stir to coat. Let the mixture stand until cool to the touch, about 2 minutes.
4 Working quickly, fold in the white chocolate and salt until just combined.
5 Scrape the mixture into the prepared baking dish and press into an even layer.
6 Let stand at room temperature until cool, about 45 minutes.
7 Using a sieve, dust with the matcha powder.
8 Cut into 3-inch squares, then serve and enjoy!
9 The treats can be stored in an airtight container for up to 2 days.
