Preheat oven to 350°F degrees prep a 8 x 8 or 9 x 9 inch baking pan by lining with parchment paper and using metal binder clips and clipping down the sides of parchment paper to hold down the paper. Set aside.
In a medium bowl, whisk together flour, baking powder, corn starch and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar on medium high speed until light and fluffy. About 2-3 minutes.
Add the egg, and mix on medium speed until incorporated. Scrape down the sides with a rubber spatula, and add the almond extract. Mix on low just until combined.
On the lowest speed, add the dry ingredients and sprinkles to the butter and sugar mixture. Mix until just combined. Do not over mix.
Transfer the cookie dough to the prepared pan and use your hands or a spatula to press the cookie dough into an even layer, pressing into the corners. I used my hands and a bowl scraper to flatten the top.
Bake the sugar cookie dough for 20-25 minutes mine took 25 minutes. (My oven runs hot) or bake until edges are slightly golden brown. The middle will look slightly underbaked, the dough will finish baking in the pan.
Remove from the oven and cool completely in the fridge for 20 minutes. While the bars are cooling, make the frosting
For the Cream Cheese Frosting
In the bowl of a stand mixer fitted with the paddle attachment, beat the softened cream cheese on medium speed until smooth and creamy. With a rubber spatula, scrape down the sides and the bottom of the bowl. Add the butter and cream on medium high speed for 1 minute.
Add the sifted powder sugar, vanilla, salt, and cream, mix on low until incorporated. Turn the speed to medium high and beat for 2 minutes.
Depending on how you like your frosting, if it’s too thin, add more powder sugar. If too thick, add a dash more heavy cream.
Once the bars have completely cooled, use an offset spatula, spread the frosting evenly over the top of the cookie bars.
Top with sprinkles.
To cut perfect sharp edges, chill the cookies before cutting into 16 squares. Serve chilled or room temperature.