Preheat oven to 350 degrees.
Using a stand mixer, cream together butter, sugar, egg, and vanilla.
Add flour, cocoa, and salt to butter mixture and mix together. Dough should be pretty sticky.
Add dough to cookie gun and press onto an ungreased cookie sheet. Top with sprinkles.
Bake 5-7 minutes and remove from oven before cookies brown. Cool on wire rack. Enjoy!