Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper or silicone mats.

In a large mixing bowl, beat together the softened butter and granulated sugar until creamy and lightened in color, about 1-2 minutes.

Add the large egg and vanilla extract to the creamed mixture, mixing until fluffy, roughly 30-60 seconds.

Incorporate the brown sugar and vegetable oil, mixing until the batter is rich and moist.

Gradually add the all-purpose flour, baking soda, and baking powder, stirring until no dry flour remains.

Fold in the Lucky Charms marshmallows, white chocolate chips, and any optional sprinkles.

Scoop the dough into balls of about 2 tablespoons each onto baking sheets, spacing them 2 inches apart.

Bake the cookies for 9-11 minutes, until golden brown around the edges and slightly glossy in the center.

Cool the cookies on the baking sheet for 3-5 minutes before transferring to a wire rack to cool completely.