Preheat your oven to 350°F (175°C).

Line two large baking sheets with parchment paper or silicone baking mats. Set aside. Ensure the butter and eggs are at room temperature.

In the bowl of a stand mixer fitted with the paddle attachment (or using a hand mixer), beat the softened butter until creamy (about 1 minute).

Add the granulated sugar to the butter. Beat on medium speed for 3 to 4 minutes until the mixture is light, fluffy, and pale yellow. Scrape down the sides of the bowl as needed.

Beat in the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract until fully combined.

In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.

With the mixer running on low speed, gradually add the dry ingredients to the wet ingredients. Mix only until just combined. Do not overmix.

Remove the bowl from the mixer. Gently fold in the ½ cup of rainbow sprinkles using a rubber spatula until they are evenly distributed. Avoid excessive mixing to prevent color bleeding.

Use a medium cookie scoop (about 1.5 to 2 tablespoons) to portion the dough. Roll the dough into smooth balls and place them two inches apart on the prepared baking sheets. (Optional: Chill the dough for 30 minutes for thicker cookies.)

Bake one sheet at a time in the preheated 350°F (175°C) oven for 9 to 12 minutes. The edges should be set and lightly golden, but the centers should still look soft.

Allow the cookies to cool on the baking sheet for 5 minutes before carefully transferring them to a wire rack to cool completely. Repeat with remaining dough.