Fit a large pastry bag with a 1/2 inch round tip.
Put the egg whites in the bowl of a stand mixer fitted with the whisk attachment.
Put 1/4 cup of water in a small bowl and sprinkle the packet of gelatin over it. Stir well.
In a small saucepan, combine the remaining 8 teaspoons of water, sugar, corn syrup and salt. Using medium heat, heat without stirring until a candy thermometer registers 240 degrees (soft ball stage).
While the syrup heats, beat the eggs with the whisk attachment until stiff peaks form. If eggs form peaks before syrup reaches 240, stop the mixer. When the syrup hits 240 degrees, turn the mixer back on and pour it into the egg whites in a thin stream. Use a rubber scraper to make sure you get it all.
Scrape the gelatin into the still-hot saucepan and stir it so that it thins and dissolves from the residual heat. Add it to the mixer while it is still going. Add the vanilla and keep on beating for 5 minutes or until bowl feels cool and mixture is thick enough to pipe.
Transfer marshmallow cream to the pastry bag.
Untwist the Oreos so that you have 40 halves, 20 with crème and 20 without. Pipe mounds of marshmallow on top of the cookies and let the marshmallow topped cookies sit on a rack for at least two hours.
After the two hours have passed, you can move on to dipping OR you can freeze the cookies and dip them when convenient.
To coat with chocolate use your favorite method or use mine.
Coating: I like to melt small amounts of chocolate in a custard cup in the microwave, use it for as many cookies as I can, then melt and repeat. For instance, I’ll fill a custard cup with chopped chocolate, throw in a dab of coconut oil if I am using chips, then melt the chocolate (high for semisweet, 50% power for milk) and stir every 30 seconds or so. To coat the cookies, set one cookie on a fork and hold it over the custard cup full of chocolate. Spoon chocolate over the top and let it drip back down in the cup. You can do it this way or use a double boiler and melt all of the chocolate at once if you prefer.
After dipping each cookie, lay it on a wax paper lined plate. Once you've filled a plate with cookies, put it in the freezer for a few minutes to set the chocolate.