Preheat your oven to 350°F.
In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
In another bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chocolate chips and mini marshmallows.
Drop tablespoon-sized balls of dough onto ungreased baking sheets, spacing them about 2 inches apart.
Bake for 10-12 minutes, or until the edges are lightly golden.
Remove from the oven and let cool on the baking sheets for 5 minutes before transferring to wire racks to cool completely.