Preheat oven to 325 degrees F. Heavily grease cookie sheets or use the non-stick liners (Silpad).
In a large mixing bowl, cream together the sugar and butter. Add salt, egg, water, and vanilla extract; beat until smooth. Beat in the flour and cocoa powder until well combined (the dough will be stiff).
Roll the dough into balls into walnut-size balls, about 1/2-inch balls. Place the balls on the prepared baking sheet. Flatten each ball until it is about 1/8-inch thick, using the bottom of a glass that has been dipped in cocoa powder.
Bake the cookies, one baking sheet at a time, for 15 minutes. Remove from oven and remove cookies from baking sheets to cooling racks. Let cookies completely cool before adding Cookie Filling.
Assemble Cookies: Spread approximately 1 to 2 tablespoons of Cookie Filling on one cookie (the recipe makes a large batch of filling, so be generous with your spreading of it). Place another cookie, equal in size to the first cookie, on top of the filling. Lightly press the two cookies together to work the filling evenly to the outside edges of the cookies. Repeat this process until all the cookies have been filled and sandwiched together.
Makes 25 to 30 Oreo-style sandwich cookies (depending on how big you make the cookies).
In a mixing bowl, cream together butter, vegetable shortening, sugar, Marshmallow Creme, and vanilla extract. Turn the mixer on high and beat for 2 to 3 minute until the mixture is light and fluffy.
* Regular unsweetened cocoa powder may be substituted.
** Marshmallow Fluff/Cream may be substituted (learn how to make).
Oreo-Style Cookies Recipe: https://whatscookingamerica.net/cookie/oreocookies.htm