Line cookie sheet with a baking paper or silicone baking liners
In a large bowl, whisk eggs till light in color.
Add water and oil and whisk again.
Fold in the cake box mix.
Make dough balls with your hands or a cookie dough scoop and place them on your baking sheet with about 2 inches of space.
Chill these dough balls for 2 hours in the refrigerator.
If using, sprinkle some sugar on top of the dough balls.
Bake at 390 F to 200 C for about 8 - 10 minutes.
Remove tray from oven and gently place cookies on cooling sheets. This will prevent the cookies from overbaking, and becoming crunchy.
Once the cookies are completely cooled, add frosting to the flat side of one cookie and place another cookie on top, so that the two flat sides are facing each other.
Notes
Spraying oil on your baking sheet will encourage the dough to spread. If you have a silicone baking sheet, it is preferable to use that.
You can also use a piping bag to pipe the batter on the baking sheet.
For a nicer-looking finish, you can pipe the frosting on the cookies with swirly patterns.