Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper to prevent sticking and ensure easy cleanup.
In a large mixing bowl, use a hand mixer or stand mixer to beat together the softened butter, granulated sugar, and packed brown sugar. Mix on medium speed until the mixture is light and fluffy, about 3-4 minutes.
Add the eggs one at a time, mixing well after each addition to ensure they're fully incorporated. Then, stir in the vanilla extract until the batter is uniform.
In a separate bowl, whisk together the sifted all-purpose flour, baking soda, baking powder, and salt until well combined.
Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; the dough should be slightly sticky but well-hydrated.
Using a spatula, gently fold in the rainbow sprinkles and white chocolate chips until they are evenly distributed throughout the dough.
Using a cookie scoop or a tablespoon, drop rounded portions of dough onto the lined baking sheets, leaving about 2 inches of space between each cookie to allow for spreading while baking.
Place the cookies in the preheated oven and bake for 10-12 minutes, or until the edges are lightly golden and the centers look just set but slightly soft. Avoid overbaking for the chewiest result.
Once baked, remove the cookies from the oven and allow them to cool on the baking sheets for 5 minutes. Afterward, carefully transfer the cookies to a wire rack to cool completely.
Notes
For a festive finish, arrange the cookies on a vibrant plate and generously sprinkle some additional confetti sprinkles on top.