0 Preheat oven to 350°F. Lightly coat a 13” x 9” metal baking pan with nonstick cooking spray and line with parchment paper to create a sling, with an overhang on all four sides.
1 Sugar Cookie Dough: In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and sugar on medium speed until fluffy and light in color, about 2-3 minutes.
2 Scrape the bowl well, then add the egg, vanilla, and almond extract while the mixer is on low speed. Mix until well combined. Scrape the sides of the bowl again, then add flour, cornstarch, baking powder, and salt. Mix just until combined.
3 Press the sugar cookie dough into the prepared pan, spreading it out evenly to the edges with a small offset spatula. Bake at 350 for 15-18 minutes, or just until the edges start to turn golden brown. Allow to cool completely before frosting.
5 Vanilla Buttercream: In the bowl of a stand mixer fitted with a paddle attachment, cream the butter on medium speed until smooth and creamy, about 2 minutes. Scrape down the bowl with a rubber spatula.
6 Add the powdered sugar, vanilla, salt, and heavy cream to the bowl. Start mixing on low speed until the ingredients are combined, so the powdered sugar doesn’t spill out. Scrape the bowl well with a rubber spatula.
7 Mix on medium-high speed for 2 minutes. The frosting should be completely smooth and creamy. Use gel food coloring to dye the buttercream.
8 Decorating: Scoop the buttercream frosting onto the cooled sugar cookie bars, then use a small offset spatula to smooth it out evenly to the edges. Top with sprinkles, slice, and enjoy!
