Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, combine the softened butter, granulated sugar, and brown sugar. Use an electric mixer to cream them together until light and fluffy.

Beat in the egg and vanilla extract until well incorporated.

In another bowl, whisk together the flour, baking soda, and salt. Gradually mix this dry mixture into the wet ingredients until just combined.

Carefully fold in the rainbow sprinkles using a spatula or wooden spoon—be gentle to avoid breaking them.

Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes or until the edges are lightly golden. Don’t overbake; they should remain soft in the center.

Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.