Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In a large bowl, whisk the melted vegan butter, light brown sugar, applesauce, and vanilla extract until smooth and creamy.
Add the dry ingredients to the wet mixture and stir until just combined. Fold in the chopped vegan dark chocolate.
Cover the bowl and refrigerate the dough for 15 minutes to firm up.
Scoop out about 2 tablespoons of dough per cookie and roll into balls. Place on the prepared baking sheet, leaving about 2 inches of space between each.
Bake for 10 minutes, until the edges are set but the centers are still soft.
Remove the cookies from the oven and gently press a marshmallow half into the center of each cookie. Return to the oven for 2–4 minutes, just until the marshmallows puff slightly.
Let the cookies cool on the baking sheet for 10 minutes, then transfer them to a wire rack to cool completely.
While cookies cool, melt the chopped semi-sweet chocolate using a double boiler, or in a microwave in 20-second bursts, stirring between intervals until smooth.
Spoon the melted chocolate over each marshmallow-topped cookie. Add sprinkles if desired. Allow the chocolate to set at room temperature for 30–60 minutes before serving.
Notes
*I cut out rounds from my marshmallows just for the look, but it’s completely optional.
To store: Once the chocolate sets, you can store these hot chocolate cookies in an airtight container with parchment paper between the layers. They’ll keep up to 1 week.