Cream the Butter & Sugar: In a large mixing bowl, beat together the butter, brown sugar, and granulated sugar until smooth.
Add the Wet Ingredients: Mix in the eggs and vanilla extract until well combined.
Prepare the Dry Ingredients: In a food processor, grind the Lucky Charms cereal (excluding marshmallows) into a fine powder.
Combine Dry & Wet Ingredients: In a separate bowl, whisk together the processed cereal, flour, baking soda, corn starch, and salt. Gradually add this mixture to the wet ingredients, stirring until just combined.
Fold in the Goodies: Gently fold in the Lucky Charms marshmallows and white chocolate chips.
Chill the Dough: Refrigerate the cookie dough for at least 2 hours for better texture and thickness.
Preheat & Prep: Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
Shape the Cookies: Let the dough sit at room temperature for 10 minutes, then scoop tablespoon-sized portions onto the baking sheet, spacing them 2 inches apart.
Bake & Cool: Bake for 10-12 minutes or until lightly golden. Cool on a wire rack before serving.