Preheat your oven to 350°F (175°C) to ensure even baking.
Melt the chopped semi-sweet chocolate bars over a double boiler or in the microwave, stirring until fully melted. Allow it to cool slightly.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.
In a large mixing bowl, beat the butter, brown sugar, and granulated sugar together until light and fluffy.
Add the eggs and vanilla extract to the butter mixture and mix until well combined.
Pour the melted chocolate into the butter mixture and mix until fully incorporated. Gradually add the dry ingredients, stirring until just combined.
Gently fold in the walnuts, half of the mini marshmallows, and half of the chopped milk chocolate bars.
Drop spoonfuls of dough onto a parchment-lined baking sheet, spacing them about 2 inches apart. Top with extra marshmallows and chocolate chunks.
Bake for 10-12 minutes, until edges are set but centers remain soft. Cool on the baking sheet for 5 minutes before transferring to a wire rack.
Enjoy your homemade Rocky Road Chocolate Cookies!
