Preheat oven to 350°F. Line a 9x13” baking dish with foil, parchment paper, or spray the pan directly with nonstick cooking spray that contains flour. If using foil, spray the foil with nonstick spray.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a hand mixer, cream the butter and sugar on medium speed for 1-2 minutes until smooth.
Add the egg and vanilla extract and almond extract, if using, and mix until combined.
Add the flour, baking powder, and salt and mix until just combined. Don’t overmix.
Scoop the cookie dough into the prepared baking dish and spread into a flat, even layer. I spray my hands lightly with nonstick cooking spray before pressing the dough in the pan.
Bake for 20-25 minutes or until the edges are set and lightly golden brown and the center is no longer shiny. If you insert a toothpick in the center there should be no dough that comes out on it. Be careful not to overbake as this will result in a drier and more crumbly cookie bar.
Remove from the oven and let cool to room temperature. Do not frost until the bars are completely cool otherwise the frosting will melt.
Make a batch of buttercream frosting for sugar cookies and spread overtop of the sugar cookie bars. Slice and serve!