Heat cream to 80 degrees C or 176 degrees F. Pour in your genmaicha, give it a gentle stir, and let sit for three minutes. The tea leaves will swell up and look as if they have absorbed all the cream. Don’t worry—they haven’t.
Pour cream into a fine-mesh sieve over a bowl. Strain out the cream, pressing the tea leaves with the back of a spoon, or your hands. You should end up with about 1 ½ cups of tea-infused cream.
In the larger pot, place ½ cup of tea-infused cream with the butter over low heat. Add in 1 cup white chocolate chips, keeping the heat low and stirring all the while until smooth. Add marshmallows and do the same. Don’t let this mixture burn or curdle—slowly but surely does it.
Stir in cereal, folding slowing and gently until it is all evenly coated.
Press the cereal mixture into the pan gently. Don’t press it too hard or you’ll have heavy, dense squares. Pop it in the fridge to firm up.
Pour the remaining 1 cup of tea-infused cream back into the smaller pot and bring just to a boil. Remove from heat. Add in the remaining 3 cups of white chocolate chips.
Place the pot back on low heat and stir gently until white chocolate chips are melted. Stir together until smooth and let sit until room temperature.
Remove the pan from the fridge. Spread ganache evenly over the squares, smoothing with a spatula until the whole surface is covered. Do NOT rush and pour while too warm or it will melt into your squares.
Decorate the top with some scattered white chocolate chips and genmaicha. Return to the fridge to firm up. Serve at room temperature.