• Heat oven to 350°F. Line an 8-inch square baking pan with foil. Spray the foil with nonstick baking spray. Set aside.

Crust

• Add 1 stick of salted butter and 1/3 cup powdered sugar to the bowl of an electric stand mixer. Using the paddle attachment, beat until the powdered sugar is no longer visible, about one minute. Add flour and mix until just combined.
• Pour dough into prepared pan. Press dough evenly into bottom of prepared pan. Bake 15 minutes. Remove from oven and allow to cool for 10 minutes on a baking rack.

Funfetti Topping

• Add corn syrup, water and vanilla extract to a small mixing bowl. Mix well with a spoon and set aside.
• Add 1 stick of salted butter, sugar and salt into same electric stand mixer bowl. Using a paddle attachment, beat at medium speed until well mixed. Add 2 eggs and beat until well mixed. Add half of flour and half of the corn syrup mixture, beating to combine thoroughly. Repeat with the remaining flour and corn syrup.
• Add sprinkles and slowly combine with rubber spatula. Pour funfetti topping over shortbread crust. Using the rubber spatula, spread it evenly over the crust. Optionally, add 1 or 2 more tablespoons of sprinkles over the topping and use the spatula to press them into the topping.
• Bake 25 to 28 minutes or until golden brown. Place pan on a cooling rack for about 10 minutes. Then, carefully remove the bars using the flaps of overlapping foil and allow bars to completely cool on baking rack. (To get the cleanest cut bars, allow them to completely cool at least a few hours or even overnight.)