Instructions

1. Prepare your ingredients and equipment: Remove butter from refrigerator to soften, measure all ingredients precisely, and preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
2. In a large mixing bowl, cream together softened butter, granulated sugar, and powdered sugar using an electric mixer. Beat on medium speed for 3-4 minutes until light and fluffy, scraping down the sides of the bowl occasionally.
3. Add the large egg and vanilla extract to the butter-sugar mixture. Mix on medium speed until fully incorporated and smooth, about 1-2 minutes.
4. In a separate bowl, whisk together all-purpose flour, baking powder, and salt to ensure even distribution of leavening agents.
5. Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Do not overmix.
6. Fold in rainbow sprinkles and white chocolate chips using a spatula, distributing them evenly throughout the dough.
7. Scoop dough using a 3-tablespoon cookie scoop or measure with a standard ice cream scoop. Place cookies 2 inches apart on prepared baking sheets.
8. Gently press down on each cookie dough ball to slightly flatten, ensuring even baking.
9. Bake in the preheated oven for 10-12 minutes, or until edges are lightly golden and centers are set but still soft.
10. Remove from oven and let cookies cool on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
11. Optional: Drizzle with additional melted white chocolate or sprinkle extra rainbow sprinkles for decoration.
12. Store cooled cookies in an airtight container at room temperature for up to 5 days. For best texture, place a piece of bread in the container to maintain softness.