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

Cream together the softened butter and granulated sugar until light and fluffy, about 2-3 minutes.

Add the egg and vanilla extract and mix until fully incorporated.

Mix in the vegetable oil and brown sugar until well combined.

In a separate bowl, whisk together the all-purpose flour, baking soda, and baking powder. Gradually add to the wet ingredients.

Gently fold in the Lucky Charms marshmallows, white chocolate chips, and optional sprinkles.

Scoop out 2 tablespoons of cookie dough for each cookie, spaced 2 inches apart on the baking sheets.

Bake for 9–11 minutes or until edges are set; do not overbake.

Let cool on baking sheets for 3–5 minutes, then transfer to a wire rack.