Heat the oven to 350°F.

Line two baking sheets with parchment paper.

Combine the chocolate and butter in a microwave-safe bowl and microwave in 20-second bursts, stirring each time, until smooth.

Let the chocolate mixture cool for 5 minutes.

In a large bowl, beat the eggs and sugar with an electric mixer on medium-high speed for 3 to 4 minutes, until pale and thick.

Beat in the vanilla.

With the mixer on low, slowly beat in the melted chocolate mixture until combined.

In a separate bowl, whisk together the flour, hot cocoa mix, cocoa powder, baking powder, and salt.

Fold the dry ingredients into the chocolate mixture just until no dry streaks remain.

Chill the dough for 20 to 30 minutes, until scoopable.

Scoop rounded 1 1/2-tablespoon portions onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 10 to 12 minutes, rotating the sheets and switching their rack positions halfway through, until the tops are crackled and the edges are set while the centers still look slightly soft.

Let the cookies cool on the baking sheets for 10 minutes.

Transfer the cookies to a wire rack to cool completely.