Preheat the oven to 350 and line a few trays with baking paper or spray with non-stick spray.
In a metal bowl, place the butter inside the bowl and place in the preheating oven.
Leave it just for a few minutes, until the butter starts to melt around the outside (approx ½ of the butter melted). Take out of oven to cool.
Once the butter has cooled, add both sugars and beat with a mixer until light and fluffy.
Add the vanilla and eggs, beating between each addition just until mixed.
Add the flour,chocolate mix, baking soda and salt or sea salt and beat on a low speed, just until combined.
Fold in the chocolate chips & mini marshmallows until just incorporated.
Use an ice cream or cookie scoop (¼ cup for large, 1.5 tablespoons for medium) and drop the dough onto the prepared baking sheets, allowing room for spreading.
Pat down cookies just a little and press additional chocolate chips & mini marshmallows on top of cookie dough if desired.
Bake one tray of cookies at a time, for 10-12 minutes for large, 8-9 minutes for small. Don't over-bake and allow to cool on wire rack.
Makes 1 dozen large or 2 dozen small cookies.
Store cookies in air-tight container.