Preheat your oven to 375°F (190°C) and line baking sheets with parchment paper.

In a large bowl, cream together the softened butter, granulated sugar, and brown sugar using an electric mixer until light and fluffy for 2-3 minutes.

Beat in eggs one at a time, then stir in vanilla extract, scraping down the bowl as needed.

In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined but not overmixed; the dough will be thick and chocolatey.

Take about 1 tablespoon of dough, flatten it, place one miniature marshmallow in the center, and carefully mold the dough around it to form a sealed ball; repeat for remaining dough and marshmallows.

For best results and to prevent spreading, chill the assembled cookie dough balls on the prepared baking sheets in the refrigerator for 15-20 minutes.

Arrange chilled cookie dough balls about 2 inches apart on baking sheets and bake for 8-10 minutes, or until edges are set and centers are slightly soft, being careful not to overbake.

Let cookies cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely, allowing the marshmallow to become gooey.