Preheat the oven to 350 degrees Fahrenheit. Line 2 cookie sheets with parchment paper or a silicone liner.
Cream together the butter and sugars in a large bowl, mix together for about 2 minutes until light in color, and creamy.
Stir in the eggs and vanilla extract.
Add in the flour, cornstarch, salt, baking soda, and crushed cereal crumbs. Stir together till you have a nice soft cookie dough.
Add in the white chocolate chips, and Lucky Charm's marshmallows, and fold them into the dough carefully.
Scoop your cookie dough into small 2 TBS sized balls. Roll into smooth balls, and place on the prepared baking tray.
Bake the cookies in the preheated oven for about 7 to 9 minutes, until the tops of the cookies are set.
Top each of the cookies with 2 to 3 lucky charm marshmallows, and about 4 chocolate chips for looks if desired.
Let the cookies cool on the cookie sheet for about 5 minutes before transferring them to a cooling rack for another few minutes before enjoying warm, or let them cool completely.