Cookie dough: Begin by placing the butter into a small bowl and microwave in 30-second intervals until melted. Next, add in the cocoa powder and espresso powder, mix together until it is lump free. Let this mixture rest for a few minutes to cool.
In a separate bowl, microwave the chocolate in 30-second intervals until fully melted. Make sure to stir between each interval, mine took about 90 seconds to get completely melted. Then, in a large mixing bowl, using a handheld mixer, combine the eggs, brown sugar, and vanilla extract and beat together on high speed for 2-3 minutes or until pale and fluffy. Scrape down the sides of the bowl and the bottom of the bowl
After that, add the melted chocolate and melted butter to the egg mixture and mix on high speed until fully combined. Scrape down the sides and bottom of the bowl again. Now, fold in the dry ingredients, the flour and salt, until they are just combined. Be gentle so that you don't knock the air out of the cookie dough. Lastly, use a large cookie scoop to create 12-13 large balls of dough, put them on parchment lined baking pan and place it in the fridge for 1 hour to chill.
Bake: Preheat the oven to 350 degrees F and once the oven is preheated place the cookie sheet into the oven and bake for 10-12 minutes.
Chocolate Ganache: Place the chocolate pieces and butter into a medium-sized mixing bowl and microwave in 30-second intervals until fully melted. Make sure to stir well between each interval. Then, add in the heavy whipping cream and mix together until fully incorporated.
Let the ganache chill in the fridge for 20 minutes while the cookies are cooling. Once the cookies have cooled and are at room temperature, spread your chocolate over the top of the cookies. Decorate the tops with chocolate rainbow sprinkles, serve and enjoy.
Cosmic Brownie Cookies make for a fantastic treat to serve during the holidays or even a birthday party. These homemade brownie cookies are jumbo cookies that are loaded with all the chocolatey goodness you could want.