Grease a 8 x 8 glass pan & dust with confectioners sugar
In stand mixer, combine ½ cup of cold water & gelatin on low speed with a whisk attachment let sit
In saucepan, combine Allulose, liquid allulose syrup, salt and ½ cup of water. Stir & cook over medium heat until sugar is dissolved. Raise heat to high, place candy thermometer in pan, stir continuously, & cook until reaches 240 F
With stand mixer on low, slowly pour heated sugar syrup in with gelatin. Place mixer on high and whip for approximately 15 minutes or until thick marshmallow whip is formed.
Lightly mix in elderflower liqueur and pour into dusted pan. Evan out with a spatula and add sprinkles. Lightly dust with more confectioners sugar and let sit for 8-9 hours to dry.
Remove marshmallow slab from pan and cut into squares with sharp knife. Dust again with confectioners sugar and enjoy.