Preheat your oven to 350°F (175°C). This ensures that the cookies bake evenly and rise properly.

In a medium bowl, whisk together the flour, baking soda, and salt. This helps to evenly distribute the leavening agent and salt throughout the flour.

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar using an electric mixer on medium speed until light and fluffy, about 2-3 minutes. This incorporates air into the mixture, which helps the cookies rise.

Add the egg and vanilla extract to the butter-sugar mixture, mixing until fully combined.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Overmixing can lead to tough cookies.

Fold in the rainbow sprinkles gently with a spatula to create a tie-dye effect.

Line a baking sheet with parchment paper to prevent sticking.

Using a cookie scoop, drop tablespoon-sized balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 8-10 minutes, or until the edges are lightly golden. The centers may look slightly underbaked; they will continue to cook on the baking sheet.

Remove the cookies from the oven and immediately press a Hershey's Kiss into the center of each cookie. The heat from the cookie will melt the chocolate slightly.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.