Start by melting the dark chocolate and heavy cream together in a double boiler over medium heat, stirring until smooth. Allow the ganache to cool and set for about 30 minutes.

In a large mixing bowl, cream together the softened unsalted butter, granulated sugar, and light brown sugar until light and fluffy, about 3-5 minutes.

Add the egg and vanilla extract to the creamed mixture, mixing on low speed until combined. Do not overmix.

In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt. Gradually fold into the wet ingredients until no dry flour remains.

Cover the mixing bowl with plastic wrap and refrigerate the cookie dough for about 1 hour.

Scoop the dough into 1.5-tablespoon portions, placing about 1 teaspoon of the cooled ganache in the center of each. Shape it into a ball.

Place the assembled cookie balls on a baking sheet and refrigerate for another 30 minutes.

Preheat your oven to 350°F (180°C). Bake the cookies for 10-12 minutes.

Once baked, allow the cookies to cool on a baking sheet for 5-10 minutes before transferring to a wire rack. Dust with powdered sugar before serving.