Line a rimmed baking sheet with parchment paper. In a small bowl, combine corn starch and powdered sugar, and whisk together. Sift cornstarch and sugar mixture evenly over the parchment paper.

Pour ½ cup water into the bowl of a stand mixer with whisk attachment. Sprinkle gelatin over the top and let it sit without stirring for 15 minutes.

Meanwhile, in a medium sauce pan, combine the remaining ½ cup water, corn syrup, sugar, and salt. Without stirring, attach your candy thermometer to the edge of your pan and bring everything to a boil over medium-high heat. Let it boil for about 8 minutes, or until the thermometer reads 240ºF.

Without turning off the mixer, slowly add matcha 1 teaspoon at a time. Continue whisking an additional 2 minutes.

Pour the marshmallow creme onto the prepared baking sheet. Spray a spatula with non-stick cooking spray and spread the creme as evenly as possible. Dust the top with more sifted cornstarch/sugar. Cover with parchment and allow to set up overnight.

To cut the marshmallows, grease a knife with non-stick cooking spray and cut into large squares.