Preheat your oven to 350 F. Line two baking sheets with parchment paper. Set it aside.

In a bowl of a stand size mixer fitted with a paddle attachment, cream the butter and both sugars until light and fluffy on medium high speed. About 3 minutes.

With the mixer on medium speed, add the egg, and and beat for 30 seconds. Add the vanilla extract, and mix just until combined.

On the lowest speed, add the flour, baking powder, baking soda, sprinkles and salt. Mix just until the flour streaks disappears. Do not over mix.

Use a large cookie scoop to portion out 9 equally sized cookie dough balls, or weigh them out to 3 ounces each.

Place 6 cookies on the sheet pan about 1 inch apart. You will use 2 sheet pans. With the bottom of your hand, gently smush down the top. You want a slightly flat top to create a flatter top for when you frost the cookie.

Bake the cookies for 11 minutes, let them cool before transferring to a cooling rack to finish cooling. While the cookies are cooling, make the buttercream.

In the bowl of an electric mixer, combine the butter and cream cheese. Cream on medium speed for about two minutes. Scrape down the sides and bottom of the bowl. Beat again for 2 more minutes.

With the mixer on low speed, add the powdered sugar, followed by the vanilla, and salt. Beat on low just until mixed. Then turn the mixer to medium high speed and beat the mixture for 2-3 minutes.

With a rubber spatula, fold in the rainbow sprinkles.

Once the cookies are completely cooled, and no longer warm, frost the cookies.

With a plastic bag or a piping bag, cut a medium size hole and frost the top of the cookie and decorate with extra sprinkles.