Start by preheating your oven to 350°F (175°C). In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until it's light and fluffy.
Add the egg and vanilla extract to the butter mixture, mixing until everything is well combined.
In a separate bowl, whisk together the flour, cheesecake pudding mix, baking soda, and salt. Gradually mix the dry ingredients into the wet ingredients until just combined.
Fold in the rainbow sprinkles, ensuring they are evenly distributed throughout the dough.
Scoop tablespoon-sized amounts of dough onto a lined baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly browned. Remove from the oven and let them cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
Notes
These cookies are best enjoyed fresh but can be stored in an airtight container for a few days!