Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a medium bowl, whisk together the all-purpose flour, Dutch cocoa powder, salt, and baking powder until well combined.

In a large mixing bowl, cream together the softened unsalted butter, light brown sugar, and granulated sugar for about 2 minutes.

Add the egg yolks and vanilla to the creamed mixture and mix for another 1-2 minutes until fluffy.

Gradually add the dry ingredients to the butter mixture, mixing until just combined.

Using a cookie scoop, portion out the dough into roughly 34 balls and place them on the prepared baking sheets.

Press down gently in the center of each dough ball to create indents.

Chill the indented cookie dough balls for at least 1 hour.

Bake the cookies for 9-11 minutes until set.

Cool the cookies on the baking sheets for about 5 minutes before transferring to a wire rack.

In a saucepan, heat the heavy whipping cream until boiling, then pour over the chocolate chips and stir until smooth.

Fill each indentation on your cookies with the silky ganache and optionally sprinkle with nonpareils.