In the bowl of your stand mixer or a large mixing bowl, beat together the softened butter, dark brown sugar, and granulated sugar until the mixture is light and fluffy. This should take about 2–3 minutes.

Add the eggs, one at a time, beating well after each addition. Then, mix in the vanilla extract until fully incorporated.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, mixing on low speed until just combined.

Gently fold in the semisweet chocolate chips, white chocolate chips, and rainbow sprinkles using a spatula or wooden spoon. Be careful not to overmix to maintain the cookies' tender texture.

Using a large cookie scoop (about 3 tablespoons), portion out the dough onto a parchment-lined baking sheet, spacing each ball about 2 inches apart. For an extra pop of color, press a few additional chocolate chips and sprinkles into the tops of each dough ball.

Refrigerate the dough for at least 30 minutes. Chilling the dough helps prevent the cookies from spreading too much during baking, resulting in thicker, chewier cookies.

Preheat your oven to 350°F (177°C).

Place the chilled dough balls onto a prepared baking sheet, leaving space between each. Bake for 13 minutes, or until the edges are golden brown but the centers still look slightly underbaked.

Allow the cookies to cool on the baking sheet for about 2 minutes before transferring them to a wire rack to cool completely. This helps them set properly and prevents breaking.