Step 1: Prep and Dry Ingredients
Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone mats. This is crucial, as melting marshmallows will fuse to an unlined pan. In a medium bowl, whisk together the flour, Dutch-processed cocoa powder, baking soda, baking powder, salt, and instant espresso powder (if using). Whisk for a full minute to ensure the leavening agents and cocoa are evenly distributed and any lumps are broken up. Set aside.

Step 2: Cream Butter and Sugars
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a hand mixer, beat the softened butter on medium speed for about 1 minute until smooth and creamy. Add the granulated sugar. Beat on medium-high speed for a full 3-4 minutes, until the mixture is very light, fluffy, and almost pale in color. This step incorporates air, which is vital for texture. Scrape down the sides of the bowl as needed.

Step 3: Incorporate Eggs and Vanilla
Add the eggs one at a time, beating well on medium speed after each addition until fully incorporated. Beat in the vanilla extract. The mixture may look slightly curdled after adding the eggs—this is normal and will come together with the dry ingredients.

Step 4: Combine Wet and Dry Ingredients
With the mixer on low speed, gradually add the dry ingredient mixture to the wet ingredients. Mix only until just combined and no streaks of flour remain. Do not overmix at this stage, as it will develop gluten and lead to tough cookies.

Step 5: Fold in the Goodies
Using a sturdy spatula, gently fold in the chocolate chips and mini marshmallows by hand. This ensures they are evenly distributed without being crushed by the mixer. The dough will be thick, sticky, and very chocolaty.

Step 6: Shape and Sugar-Coat the Dough
Place the confectioners’ sugar in a small, shallow bowl. Using a 2-tablespoon cookie scoop (or a spoon), portion out the dough and roll it into a rough ball between your palms. Immediately roll the dough ball generously in the confectioners’ sugar until completely coated. Place the sugared dough balls at least 3 inches apart on the prepared baking sheets. The cookies will spread significantly.

Step 7: Bake, Cool, and Serve
Bake one sheet at a time on the center oven rack for 11-13 minutes. The cookies are done when the edges look set and the surfaces are crackled. The centers will still look very soft—this is correct! They will firm up as they cool. As soon as you remove the pan from the oven, you can gently press a few extra mini marshmallows onto the tops of the hot cookies for extra visual appeal; they will stick and soften slightly.
Let the cookies cool on the baking sheet for 5 minutes. During this time, they will finish setting. Then, using a flat spatula, carefully transfer them to a wire cooling rack to cool completely. The marshmallows will be extremely hot and sticky, so be cautious. Dust with a little more confectioners’ sugar just before serving for that “snowy” finish