Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a large bowl, cream 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, then stir in the vanilla extract.
Gradually add the flour mixture to the wet ingredients, mixing until just combined.
Fold in the chocolate chips and mini marshmallows until evenly distributed.
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake for 10-12 minutes or until the edges are lightly golden. The centers may look slightly underbaked; they will firm up as they cool.
Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to wire racks to cool completely.