In a medium bowl, whisk together the flour, baking powder and salt. Set aside.
In a large bowl, using an electric mixer or a stand mixer, beat room temperature butter, pudding mix and sugar together until combined and light and fluffy.
Add egg and milk then beat until smooth.
Gradually add the dry ingredients into pudding mixture and mix until well combined.
Stir chocolate chips into dough.
Divide dough in half and on a lightly floured surface, roll each dough into about 6 inch rolls.
Wrap in plastic wrap and place in the fridge for at least 4 hours or overnight.
Slice cookies into 1/2 inch slices and place on an ungreased baking sheet.
Preheat oven to 375° and bake cookies for 9-10 minutes.
Remove from oven and let cookies cool for a couple minutes on baking sheet then transfer cookies to a wire rack to cool completely.
In a medium bowl, add melted butter and cocoa powder and mix until combined.
Gradually add half of the powdered sugar and half of the milk into bowl and beat, then add remaining powdered sugar and milk and beat until combined.
Pour vanilla into mixture and beat until incorporated.
Frost cookies once they have cooled completely.
Optional: Top with sprinkles of your choice.