Preheat oven to 350 degrees. Line baking sheets with parchment paper and spray the parchment with cooking spray.
Place the nuts on a baking sheet and toast for 7 minutes. Let cool completely. Chop nuts into pieces the same size as your milk chocolate chips.
Place the butter, bittersweet chocolate, and unsweetened chocolate in a microwave-safe bowl. Microwave for 30 seconds, stir, and repeat until chocolate is melted and mixture is smooth.
Sift the flour, baking powder, and salt into a small bowl.
Using a mixer, beat the eggs and sugar on medium speed for about 3 minutes. Add vanilla and melted chocolate mixture, continue beating for another 2 minutes. Scrape down the sides of the bowl as necessary. Add flour mixture, mix until just incorporated. Fold in the toasted and chopped nuts, milk chocolate chips, and marshmallows. Chill dough in fridge for thirty minutes, or until firm enough to hold its shape.
Using a 1 3/4-inch diameter scoop drop spoonfuls of dough onto prepared baking sheets. With the bottom of a measuring cup sprayed with cooking spray, gently flatten the dough mounds.
Bake for 10-12 minutes, or until the tops crack and look shiny. Cool for 10 minutes before removing them from the baking sheets. Store in an airtight container at room temperature for up to 3 days.