1-In a bowl, whisk together the flour,: In a bowl, whisk together the flour, baking soda, and salt. Set aside.
2-In a large bowl, beat the butter: In a large bowl, beat the butter and sugars until light and fluffy, about 2 minutes. Beat in the egg, egg yolk, and vanilla until combined.
3-Gradually stir the flour mixture into the: Gradually stir the flour mixture into the butter mixture until just combined. Then, gently stir in the chocolate chips and 3/4 cup of the mini marshmallows.
4-Cover and refrigerate the dough for at: Cover and refrigerate the dough for at least 30 minutes or up to 2 hours.
5-Preheat the oven to 325 degrees Fahrenheit: Preheat the oven to 325 degrees Fahrenheit. Line baking sheets with parchment paper.
6-Roll the chilled dough into 1: Roll the chilled dough into 1.5-tablespoon-sized balls. Place on baking sheets about 2 inches apart.
7-Bake for 10 minutes: Bake for 10 minutes. Then, remove them from the oven and quickly press 3 to 4 of the remaining mini marshmallows into the top of each one.
8-Return the baking sheet to the oven: Return the baking sheet to the oven. Bake for 2 to 3 minutes more until the edges are lightly browned. The cookies may look a bit underdone in the center.
9-Cool on the baking sheets for 10: Cool on the baking sheets for 10 minutes, then transfer to a wire rack to cool completely. The marshmallows will set into the cookies as they cool. Enjoy!