Add the dry ingredients into the egg mixture and mix until almost fully incorporated. If desired, you can use a mixer fitted with the paddle attachment to combine. Or, just use a spatula. Add in the melted butter, and mix to incorporate.
Add the chocolate chips and marshmallow bits in and using a spatula, mix to evenly incorporate.
Grab the frozen marshmallows from the freezer and slice them in half (if not already sliced). Using a large cookie scoop, scoop up about 3 tablespoons of cookie dough.
With damp hands, place the cookie dough into your hand and make an indent in the middle pressing the dough outwards.
Place half of a frozen marshmallow into the cookie well/indent and then form the rest of the dough around the marshmallow, closing it up. Repeat until all of the dough is used up.
Add the dough balls to the prepared baking sheet leaving 2″ apart. Bake for 11-14 minutes or until the cookie is set but still slightly soft. They will firm up while cooling.
Allow the cookies to rest on the tray for at least 10 minutes before transferring them to a cooling rack. Cool completely before storing in an air-tight container.