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

In a mixing bowl, whisk together the flour, baking powder, baking soda, and salt.

In another bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the birthday cake mix, sprinkles, and white chocolate chips until evenly distributed.

Using a cookie scoop, drop rounded tablespoons of dough onto the prepared baking sheet, leaving space between each cookie.

Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden but the centers are still soft.

Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.