Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper; this helps prevent sticking and makes cleanup a breeze. In a medium bowl, whisk together the all-purpose flour, baking powder, and salt until well combined. Set aside.

In a large mixing bowl, using an electric mixer (handheld or stand), cream together the softened unsalted butter and granulated sugar on medium speed until light and fluffy, about 2-3 minutes. Make sure to scrape down the sides of the bowl as needed.

Beat in the large eggs, one at a time, mixing well after each addition. Once combined, stir in the vanilla extract until just incorporated. Don't overmix at this stage!

Gradually add the dry flour mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; overmixing can lead to tough cookies. The dough will be soft.

Gently fold in the rainbow sprinkles with a rubber spatula until evenly distributed throughout the dough. Again, avoid overmixing to keep the colors vibrant and prevent them from bleeding too much.

Drop rounded tablespoons (or use a 1.5 tbsp cookie scoop) of dough onto the prepared baking sheets, leaving about 2 inches between each cookie. Bake for 8-10 minutes, or until the edges are lightly golden and the centers are just set but still look soft. The cookies won't spread a lot but will puff up nicely.

Let the cookies cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely. This helps them firm up and prevents breakage. Enjoy your colorful creations!