In a large bowl or stand mixer, cream together the softened unsalted butter, granulated sugar, and packed light brown sugar until light and fluffy, about 3-5 minutes.

Beat in the eggs one at a time, allowing them to fully blend before adding the next. Stir in the vanilla extract.

In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.

With the mixer on low speed, gradually add the dry ingredients to the wet mixture, mixing just until combined.

Gently fold in the chocolate chips, mini marshmallows, and any chopped nuts if desired.

Cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes.

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

Drop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches between each cookie.

Press a few mini marshmallows onto the tops of the cookies before baking if desired.

Bake in the oven for 9-11 minutes, or until the edges are golden brown and the centers are slightly soft.

Allow the cookies to cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.