Preheat your oven to 375°F (190°C) and line two baking sheets with parchment paper.

Combine the semi-sweet baking chocolate and unsalted butter in a microwave-safe bowl, heating in 30-second intervals until smooth.

Sift together the all-purpose flour, baking powder, salt, and Dutch-process cocoa powder in a separate bowl.

In a large bowl, beat the eggs, light brown sugar, vanilla extract, and peppermint extract until well combined and fluffy.

Gradually pour the cooled chocolate mixture into the egg mixture and stir until fully incorporated.

Slowly add the sifted dry ingredients into the wet ingredients, mixing until just combined.

Gently fold in the semisweet chocolate chunks until evenly distributed.

Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

Scoop heaping tablespoons of dough, roll into balls, and place on the prepared baking sheets.

Bake the cookies for 9 minutes, then add a marshmallow half on top of each cookie and return to the oven for an additional 2-3 minutes.

Let the cookies cool slightly before transferring to a wire rack, then drizzle with optional chocolate sauce and sprinkle with crushed peppermint candy.