1. Preheat the oven to 350°F. Line a 9×13 pan with foil and coat with nonstick spray. Set aside.
2. In a large bowl, whisk together the butter and sugar. Add the vanilla, eggs, and salt and whisk until smooth. Using a rubber spatula, stir in the flour until just combined. Finally, stir in the sprinkles.
3. Spread the batter into the prepared pan.
4. Bake for 25-30 minutes until the edges are set. The bars might seem underdone, but allow them to cool completely.

Frosting

1. In the bowl of the stand mixer, beat the butter for 1-2 minutes until it’s smooth. Turn the mixer to low and slowly add in the powdered sugar. Next, add 2 tablespoons of milk and mix on medium speed until creamy, scraping down the sides as necessary. If the frosting is too stiff, add in 1 more tablespoon of milk until the desired consistency is reached. Finally, add in 1-2 drops of blue food coloring and mix until a pale blue color is reached and evenly mixed.
2. Pipe or spread the frosting on top of the bars.
3. Garnish with more sprinkles if desired.