Soft, gooey chocolate chip cookies loaded with toasty mini marshmallows. Chewy centers, crisp edges, and a hint of flaky salt make these treats irresistible.
Preheat oven to 350°F. Line 2 baking sheets with parchment paper.
In a large bowl, beat softened butter, granulated sugar, and brown sugar until light and fluffy, about 2 to 3 minutes.
Beat in eggs one at a time, then mix in vanilla. Scrape the bowl.
Whisk flour, cornstarch, baking soda, and fine sea salt in a separate bowl. Add dry ingredients to the wet on low speed just until combined.
Fold in chocolate chips and 1.5 cups of the mini marshmallows, reserving 0.5 cup for topping.
Chill the dough for 20 minutes to firm slightly and minimize marshmallow melt.
Scoop dough into 2 tablespoon portions and arrange on prepared sheets, spacing about 2 inches apart.
Press a few reserved marshmallows onto the top of each dough ball or tuck them into the center so they are mostly enclosed.
Bake 9 to 11 minutes until edges are set and lightly golden but centers are still soft. Rotate pans halfway through.
Immediately sprinkle with flaky sea salt if using. Cool on the pan for 5 minutes, then transfer to a rack to cool completely.
Notes
For the gooiest centers, tuck marshmallows into the middle of the dough so they do not touch the pan directly. Store cookies airtight at room temperature for up to 3 days or freeze baked cookies for up to 2 months.