Preheat the oven to 350°F (180°C). Line a cookie sheet with parchment paper and set aside.
In the bowl of a stand mixer or with an electric hand mixer, combine the butter, powdered sugar and egg until smooth and creamy.
1 cup (222g) salted butter, softened, 1 1/4 cup (134g) powdered sugar, 1 egg
Add the vanilla, mixing until evenly distributed.
1 tsp vanilla
Next, add the cake flour, cocoa powder, baking powder and salt. Mix until a sticky dough forms. Allow the dough to rest for 5 or so minutes– it will be easier to handle that way.
2 1/4 cups (295g) cake flour, 1/3 cup (40g) dutch processed cocoa powder, 1 tsp baking powder, 1/2 tsp salt
Fold the mini marshmallows in until incorporated.
1/2 cup (17g) tiny marshmallow bits
Portion out the dough into small, 1/2 Tbsp portions. Roll into a ball and arrange on the cookie sheet.
Bake at 350°F (180°C) for 7-9 minutes, or until the cookies have spread slightly and look dry on the top.
While the cookies are baking, make the icing by combining the butter and vegetable shortening until smooth.
2 Tbsp butter, 1/2 Tbsp vegetable shortening
Add the powdered sugar and milk to bring the mixture together into a thick frosting.
3/4 cup (80g) powdered sugar, 1/8 cup milk
While mixing, add in the clear vanilla extract. Add in extra milk to thin out the icing, if needed.
1/2 tsp clear vanilla extract
Allow the cookies to cool for 5 minutes and then drizzle the top with the icing.
Allow the cookies to cool and enjoy!