Start by softening your butter to room temperature. Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper or silicone mats.
Using an electric mixer, beat together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 3-4 minutes.
Beat in the eggs one at a time, fully incorporating each before adding the next. Then add vanilla extract and mix until combined.
In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt for even distribution.
Gradually add the dry ingredients into the wet mixture, mixing on low speed or folding by hand until just combined.
Gently fold in the chocolate chips evenly throughout the dough.
Scoop about a tablespoon of dough and flatten slightly. Place 2-3 mini marshmallows in the center, then top with another tablespoon of dough. Seal edges to form a ball.
If using, press crumbled turkey bacon lightly on the outside of each cookie dough ball for a savory crunch contrast.
Place cookie dough balls on prepared baking sheets about 2 inches apart. Bake for 10-12 minutes, until edges are set but centers look slightly soft.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to let marshmallows settle inside without oozing out.