Preheat the Oven:

Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal, or lightly grease with non-stick spray.

Cream the Butter and Sugars:

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.

Add Eggs and Vanilla:

Beat in the eggs, one at a time, followed by the vanilla extract. Mix until fully combined.

Combine Dry Ingredients:

In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the Mix-ins:

Gently fold in the white chocolate chips and rainbow sprinkles, ensuring they are evenly distributed throughout the dough.

Press into the Pan:

Spread the dough evenly into the prepared baking pan, pressing it into an even layer with a spatula or your hands.

Bake:

Bake in the preheated oven for 20-25 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out clean or with a few moist crumbs.

Cool and Cut:

Allow the bars to cool completely in the pan before lifting them out using the parchment paper overhang. Cut into squares or bars as desired.