Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving overhang on two sides, and lightly spray with nonstick spray.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt until evenly combined.
In a large bowl, beat softened butter and sugar with an electric mixer on medium speed for 2-3 minutes until pale and fluffy. Scrape down sides as needed.
Add the egg, egg yolk, vanilla extract, and almond extract (if using). Beat on medium until smooth and slightly lighter in color. Scrape down the bowl.
Add the flour mixture in two batches, mixing on low speed just until no streaks remain. Do not overmix.
Press the thick dough evenly into the prepared pan. For a smooth top, place parchment over the dough and press flat with your hands or a measuring cup.
Bake for 18-22 minutes until edges are light golden and the center still looks slightly underbaked. Do not overbake.
Cool completely in the pan on a wire rack for about 1 hour before frosting.
For the frosting, beat softened butter until smooth. Gradually add powdered sugar on low speed, then increase to medium. Add cream, vanilla, and salt and beat 2-3 minutes until light and fluffy.
Spread frosting evenly over cooled bars with an offset spatula. Add sprinkles while frosting is soft. Let set for 15 minutes.
Use the parchment overhang to lift the slab onto a cutting board. Slice into 24 even squares with a sharp knife, wiping the blade clean between cuts.