Preheat the oven to 375°F (190°C). Line two baking sheets with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.
In a large bowl, using an electric mixer, beat the softened unsalted butter, granulated sugar, light brown sugar, and vanilla extract until creamy and smooth, about 2 minutes.
Add the eggs one at a time, beating well after each addition.
Gradually add the flour mixture to the butter mixture, mixing on low speed until just combined.
Stir in the semisweet chocolate chips by hand using a spatula.
Gently fold in the mini marshmallows, ensuring they are evenly distributed but not broken up.
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake in the preheated oven for 10 to 12 minutes, or until the edges are golden brown but the centers remain soft.
Remove the cookies from the oven and let them cool on the baking sheets for 5 minutes before transferring to wire racks to cool completely.