Preheat oven to 350 degrees and line a cookie sheet with parchment paper. In a large mixing bowl or the bowl of a stand mixer, cream the butter, sugar and brown sugar until light and fluffy. Add eggs one at a time, fully incorporating the first before adding the next. Add the vanilla and stir to combine.

Sift together the flour, cocoa, baking soda and salt. Add the dry ingredients to the wet ingredients and stir just until the dry ingredients are incorporated. Add the mallow bits and stir to combine.

Drop dough by heaping tablespoons full onto prepared baking sheet. Sprinkle the top of cookie dough with a few of the mallow bits. Bake cookies for 8–9 minutes until the tops are crackled and the edges are firm.

Remove from oven and allow cookies to cool on the pan for 2 minutes before transferring to a rack to cool completely.