Preheat your oven to 350 degrees F and line two baking trays with parchment paper. 

In a stand mixer using the paddle attachment, add the butter with the sugar and mix until light yellow in color and fluffy, about 5 minutes.

Mix in the egg and vanilla extract. Scrape down the sides as needed.

In a medium-sized mixing bowl whisk together flour, cocoa powder, baking powder, and kosher salt.

With the mixer on medium-low speed carefully add the flour mixture.

Mix until combined making sure to scrape down the sides and the bottom of the mixing bowl. The batter is ready when the paddle of the mixer has pulled in all the dough. This is a thicker dough.

With a cookie scooper, scoop one cookie at a time.

With your hands, take the dough and roll it into a ball.

Place the cookie on the baking sheet, and with a ¼ teaspoon, press down in the middle to make a gap. I recommend putting some non-stick spray on the spoon so it doesn’t stick to the dough. 

Once they are all done, place them in the oven for 15 to 18 minutes, until the bottom is a bit golden.

Meanwhile, prepare the ganache.

Once they are completely cooled, fill the gap with chocolate ganache using a piping bag. 

Let them cool for a couple of hours in the refrigerator before serving.

In a small saucepan set over medium-low heat add the heavy whipping cream.

Gently warm the cream without letting it boil.

Place the chocolate chips in a heatproof bowl.

Once the cream is hot, pour in the chocolate chips.

Let it rest for  2 - 3 minutes until the chocolate has softened. 

Slowly stir until completely combined and all the chocolate has melted. 

Allow the ganache to cool for 10 minutes before using.