Grease a 9x13" pan with butter then dust with powdered sugar (tap out excess powdered sugar from pan).
Stir 1/2 cup of water with gelatin and allow to bloom.
Heat sugar and the other 1/2 cup of water in a small pot until dissolved. Add the gelatin into the pot and bring to a boil while stirring. Once bubbling, take off heat, add salt and stir (it will turn whitish - make sure sides are scraped down as well). Cool to room temp.
Once cool, add vanilla and pour into a stand mixer (the cooled mix will look translucent and yellowy).
Beat on high for 6 mins, the coagulated stuff will magically turn white and fluffy! Stop and add matcha powder and beat for 2-3 mins more.
Dump into a prepared pan. I mean dump, because the mixture will be sticky and difficult to handle. Smooth out the layer as evenly as you can. Let cool and dry overnight.
Cut into squares.
Note: Always wipe your knife or plastic when slicing so it doesn't stick too badly.
Toss marshmallows into a half and half mix of matcha powder and powdered sugar. Allow to dry on a rack for a few hours.
Assemble s’mores with graham crackers, dark chocolate, and your homemade marshmallows.