Make the Marshmallow Sauce: Combine the 1/4 cup water, corn syrup, and sugar in a saucepan fitted with a candy thermometer. Bring to a boil and boil to "soft ball" stage, or about 235 degrees F.
Meanwhile, whip the egg whites until soft peaks form. Sprinkle the gelatin over the 2 tablespoons water and let dissolve.
When the syrup reaches 235 degrees F, remove it from the heat, add the gelatin, and swirl to mix. Pour the syrup into the whipped egg whites while they are still whipping. Add the vanilla and continue whipping until stiff. Let sit to cool, then thin with hot water, if necessary.
Make the Waffles: Preheat the waffle iron.
In a mixer with a whisk attachment, whip the whites until soft peaks form; then add the sugar and continue whipping until stiff.
In a separate bowl or in a blender combine the yolks, milk, flour, cocoa powder, and melted butter and mix until smooth. Fold in the whipped whites. Cook waffles according to manufacturer's instructions.
Serve with marshmallow sauce over the top and a sprinkling of confectioners' sugar.