Preheat the oven to 350 degrees. Line your baking sheet(s) with parchment and set aside.

For the cookies - in the bowl of a stand mixer, combine the softened butter and brown sugar. Cream until smooth.

Add in the egg and vanilla. Mix to combine.

Add in the salt, baking soda and flour. Mix just until the dry ingredients are combined.

Fold in the white chocolate chips and marshmallows until evenly incorporated.

Use an ice cream scoop to divide out the dough and place on the prepared baking sheets at least 2 inches apart.

Bake in the preheated oven for 10-12 minutes or until the edges are golden brown and the centers are set.

Allow to cool completely before frosting.

For the frosting - in the bowl of a stand mixer, combine the cream cheese, butter and marshmallow fluff. Mix until combined.

Add in the powdered sugar and vanilla. Mix on low speed until combined.

Bump up the speed and mix on medium for an additional minute or until the frosting is smooth and fluffy. Scrape down the sides often and mix again.

Transfer the frosting to a piping bag.

Once the cookies are cool, pipe a spiral of frosting on each cookie.

Decorate with additional marshmallows.