Filling

1. In a medium bowl, using a hand-held or stand mixer fitted with a paddle attachment, beat the butter, powdered sugar, vanilla, and salt on medium-high speed until smooth and creamy, about 2 minutes.
2. Drop teaspoonfuls onto a parchment-lined plate and place the filling into the freezer for 5 minutes.
3. Remove the filling from the freezer and roll each teaspoonful into a ball. Place the frosting into the refrigerator while preparing the cookie dough.

Funfetti Cookies

1. Preheat oven to 375°F/190°C.  Line two baking sheets with parchment paper or silicone baking mats. Set aside.
2. In a medium bowl, whisk together flour, baking soda, and salt. Set aside.
3. With a mixer, beat the butter on medium speed until completely smooth and creamy. Add the sugars and mix on medium speed until light and fluffy, about 2-3 minutes.
4. Mix in the egg until combined, and scrape down the sides and bottom of the bowl. Add the vanilla and mix until combined.
5. With the mixer on low speed, slowly add the flour mixture until combined and there are no dry spots of flour. Add sprinkles and mix until just combined. Do not over-mix.
6. Using a 2-tablespoon scoop, portion out the cookie dough and roll each into a ball. Using your thumb, make an indent into one cookie dough ball.
7. Remove the frosting from the refrigerator and place one frosting ball inside the indentation. Cover with another cookie dough ball and mold the two portions of dough around the filling. Repeat with remaining cookie dough and filling.
8. Place stuffed cookie dough 3 inches apart from each other on the prepared baking sheet pans.  Bake for 8-10 minutes or until the edges are lightly golden brown and the centers are still soft.
9. Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.