Pre-heat oven to 350 degrees; line baking sheets with parchment paper and set aside
Place semi-sweet and unsweetened chocolate with butter in a microwave-safe bowl
Microwave the ingredients for a minute and stir; microwave again for 30-second increments until everything is almost melted; stir the remaining lumps until smooth (alternatively, you can melt the butter and chocolate in a heavy duty pop over medium heat stirring constantly); set aside
In a medium bowl, whisk together dry ingredients (flour, baking powder, and salt) and set aside
In the large bowl of a stand mixer, combine eggs, sugars and vanilla; beat on high speed for about 5 minutes or until mixture is light and pale in color
Reduce the speed of your mixer and add in melted chocolate
When that is well-combined, stir in flour mixture but do not over-mix; stir in chocolate chips and marshmallows
Use a large cookie dough scoop and place dough on a baking sheet lined with parchment paper, 1-2 inches apart;
Bake cookies for 12 minutes and set aside on a wire rack to cool
Notes
Recipe can be doubled Store cookies at room temperature up to 5 days in a ziplock bag or freeze for up to two months; separate layers of cookies with parchment paper to avoid sticking
Recipe by Keep It Sweet Desserts at http://www.keepitsweetdesserts.com/hot-cocoa-cookies/