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

In a medium bowl, combine the flour, cocoa powder, baking powder, and salt. Set aside.

In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until smooth.

Add the vanilla extract and egg, mixing until well combined.

Gradually mix the dry ingredients into the wet mixture until a thick, slightly sticky dough forms.

Roll the dough into 1-inch balls and place them on the baking sheet with enough space in between.

Use your thumb or a spoon to make an indentation in the center of each dough ball.

Bake for 10-12 minutes, keeping an eye on them as they should remain soft in the center.

Heat the heavy cream in a saucepan until boiling, then pour it over the chocolate chips in a separate bowl.

Let it sit for 2 minutes before stirring gently until smooth.

Once cookies are cooled, generously fill the thumbprint indentations with ganache.

Allow the ganache to set for about 15-20 minutes before serving.