Sprinkle half the toasted coconut in an 8 by 12 inch non-metal pan.
Combine the gelatin and 1/2 cup of cold water in the bowl of an electric mixer fitted with the whisk attachment and allow to sit while you make the marshmallow syrup.
Add the sugar, matcha powder, corn syrup, salt, and 1/2 cup water in a small saucepan and cook over medium heat until the sugar dissolves. Raise the heat to high and cook until the syrup reaches 240° on a candy thermometer. Remove from the heat immediately.
With the mixer on low speed, slowly pour the sugar syrup into the dissolved gelatin. Put the mixer on high speed and whip until the mixture is very thick, about 15 minutes. Add the vanilla and mix thoroughly.
Pour in the marshmallow batter and smooth the top of the mixture with damp hands. Sprinkle on the remaining toasted coconut.
Allow to dry uncovered at room temperature at least 8 hours or overnight.
Remove the marshmallows from the pan and cut into squares. Roll the sides of each piece carefully in confectioners' sugar or remaining coconut.
Notes
Store in an airtight container for up to three months.
Wet the knife between each cut for cutting ease.
Fill the sticky marshmallow pot with hot water and boil to clean. I stick the measuring cup and thermometer in. After boiling, pour the water into the mixer bowl to melt away marshmallow.