Line your baking pan with parchment paper and clip it down if needed. This makes it easier to lift the bars out after baking and ensures even edges.
Whisk together flour, baking powder, cornstarch, and salt in a bowl. Sifting helps prevent lumps and keeps the cookie texture light.
Using a mixer, beat butter and sugar until fluffy. This step is key for a soft, tender base that melts in your mouth.
Mix in the room-temperature egg, vanilla, and almond extract until fully incorporated. Scrape the bowl to ensure no streaks of butter remain.
Add your dry mixture on low speed just until combined. Over-mixing can make the bars tough, so stop once everything is incorporated.
Transfer the dough to your prepared pan. Press it evenly with a spatula or your hands for smooth, flat bars that bake uniformly.
Bake at 350°F (175°C) for 20-25 minutes, until edges are slightly golden but the center is soft. The bars will finish baking in the pan, so don’t overbake.
Beat cream cheese until smooth, then add butter and mix for a minute. Gradually add powdered sugar, vanilla, and a pinch of salt, beating until creamy. Adjust thickness with more sugar or cream if needed.
Once the bars are fully cooled, spread frosting evenly with an offset spatula. Sprinkle festive decorations on top and chill briefly for clean cutting.
Chill bars for sharper edges, then slice into 16 squares. Serve at room temperature or slightly chilled.