Preheat the oven to 350 degrees F.
Combine the flour, baking soda, and baking powder together in a large mixing bowl.
Mix the softened butter, granulated sugar, brown sugar, vanilla extract, and egg together in a separate bowl.
Pour the liquid ingredients into the dry ingredients and mix until just well combined.
Mix in the chocolate chips.
Chill the dough for about 1 hour (optional).
Spoon the cookie dough on to baking sheets to create 18-20 cookies.
Add the marshmallow pieces to each cookie (about 2-3 pieces each).
Sprinkle each cookie with a little bit of salt.
Bake each batch for 10-12 minutes.