Preheat oven to 350 degrees Fahrenheit.
Using a stand mixer fitted with the paddle attachment, beat the butter on medium speed until smooth. Add both brown sugar and white granulated sugar to the bowl. Beat until well combined, about 2 minutes until smooth and creamy). Scrape down the sides of the bowl.
2 sticks Unsalted butter, 1 cup brown sugar, ¾ cup granulated sugar
Add the vanilla extract then the eggs one at a time, continue to scrape the bowl as necessary.
2 large eggs, 1 teaspoon vanilla extract
Combine flour, baking soda, and salt in a medium bowl and set aside.
2-⅓ cups All-purpose flour, ¾ teaspoon baking soda, 1 teaspoon Salt
Add the dry ingredients and mix on low speed to combine. Then, mix in the chocolate chips and mini marshmallows. Mix just enough until incorporated.
1 cup mini marshmallows, 2 cups chocolate chips
Remove the bowl from the mixer and fold the dough with a spatula to be sure that the ingredients are evenly mixed. Using a medium cookie scoop begin to scoop cookie dough on to a parchment lined baking sheet, keeping the cookie dough at least 2 inches a part. Add additional chocolate chips and mini marshmallows on top.
2 cups chocolate chips, 1 cup mini marshmallows
Place baking sheets in the refrigerator for at least 30 minutes.
Remove baking sheets from the refrigerator and bake for 10 minutes. Let cool slightly on the cookie sheet until firm and cool. Enjoy immediately or place in a container.