01 -
Preheat oven to 400°F (200°C). Line baking sheets with parchment paper.
02 -
In a large bowl, beat cold butter with light brown and granulated sugars until light and creamy, about 3 to 4 minutes.
03 -
Add eggs one at a time, mixing well after each addition until fully incorporated.
04 -
In a separate bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
05 -
Gradually add dry ingredients to wet mixture, mixing until just combined.
06 -
Gently fold in chocolate chips, white chocolate chunks, toasted walnuts, and mini marshmallows.
07 -
Using a large cookie scoop or hands, shape dough into ¼ cup-sized balls. Chill in refrigerator for at least 30 minutes.
08 -
Arrange 4 to 6 dough balls per baking sheet and bake for 10 to 11 minutes until edges are set but centers appear soft.
09 -
Let cookies rest on baking sheet for 10 minutes before transferring to a wire rack to cool completely or serve warm.