Place the gelatin in a small bowl and stir in the 8 tablespoons of cold water. Set aside. Spray an 8×8 pan with nonstick spray, then sprinkle some powdered sugar in the pan and shake well, dispersing it all over the pan, covering the entire thing.
In a small saucepan, combine the remaining cold water and sugar. Heat oven medium heat, stirring constantly until the sugar is dissolved and bubbly, about 3-4 minutes. Stir in the gelatin mixture, stirring, and bring it to a boil. Once boiling, immediately remove from heat. Add to the bowl of an electric mixer attached with a whisk. Let sit and slightly cool. Add in vanilla extract, beans and salt. Beat on medium-high speed for 10-15 minutes, until white and glossy and shiny and thick. Spread in the 8×8 pan and top with powdered sugar if desired. Let sit for about 4 hours, or even overnight.
To cut, I run a knife along the outside of the pan, then turn it over and shake the marshmallow cube out. Using a knife sprayed with nonstick spray, slice the marshmallows into your desired size.