Preheat the oven to 350°F. Line two large baking sheet pans with parchment paper, set aside.
In a large bowl stir together the flour, cocoa powder, baking powder. Set aside.
In the bowl of a stand mixer with the paddle attachment (or in a large bowl using a handheld electric mixer) cream together the butter with the granulated sugar and brown sugar for 3 minutes until light and fluffy.
Add the eggs one at a time. Mix together fully before adding the next egg.
Mix in the vanilla extract.
In three batches, add the flour mixture, making sure it mixes in all the way before adding the next batch. Scrape down the sides as needed.
Finally, stir in the chocolate chips.
Portion the cookie dough into 12 even-sized portions.
Roll them into a smooth ball and place them on the sheet trays about 6 inches apart. These cookies will spread quite a bit while baking so you may have to bake in batches depending on the size of your sheet pans.
Gently press down on the cookie dough balls and flatten them out into a large flat circle.
Bake for 12-14 minutes until they appear dry in the center of the cookies.
Let the cookies cool completely on the sheet pans, then transfer them to a wire rack.
While the cookies are cooling, make the frosting. Place the butter into the body of a stand mixer with the paddle attachment (or with an electric) hand mixer. Whip on medium speed until smooth.
Add the melted chocolate chips and mix until combined.
Add the powdered sugar a little at a time until fully mixed in, scrape down the sides as needed.
Add the vanilla extract, stir to combine.
Finally, start with adding 1 tablespoon of the heavy cream and mix in until fully combined. Then turn the mixer to a medium-high speed and whip it until light and fluffy (about 3 minutes.) If it is too thick to pipe, add an additional tablespoon of heavy cream (or more) until you’ve reached the desired consistency.
Using an open star tip, pipe the frosting in a spiral shape onto the tops of the cookies, serve immediately.
Notes
Feel free to use an offset spatula or butter knife to spread the frosting on if you don't wan to pipe it.
Don't overbake your cookies, they'll appear dry on the top when they're done.
Cookies should be stored at room temp in a container for up to 3 days or in the refrigerator for up to 5 days. You can freeze them for up to 3 months. Best enjoyed at room temp.
Milk can be used instead of heavy cream in the frosting if desired.
If you choose to use unsalted butter in the cookie batter, you’ll need to add a teaspoon of salt to the mix.