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 process cocoa powder, salt, and baking powder.

In a large mixing bowl, use an electric mixer to cream together the softened unsalted butter with both light brown and granulated sugars for about 2 minutes.

Add the egg yolks and the vanilla bean paste or extract to the creamed butter and sugars, mixing until pale and airy for 1-2 minutes.

Gradually add the prepared dry mixture to the wet ingredients, mixing on low speed until just combined.

Using a cookie scoop, portion out about 34 balls of dough and place these on the lined baking sheets, creating indentations in the center.

Cover the baking sheets with plastic wrap and refrigerate the dough for at least 1 hour.

Bake for 9-11 minutes, monitoring to ensure they remain soft in the center.

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

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

Once cooled, fill each indentation with the ganache and top with nonpareils if desired.