Preheat your oven to 350°F (176°C). Take an 8x8 inch baking pan and line it with parchment paper, ensuring some overhang for easy removal later.
In a mixing bowl, add the softened butter. Using a hand mixer or a sturdy spatula, cream the butter until it's smooth and creamy.
Gradually add the powdered sugar to the creamed butter. Mix it well until the sugar is fully incorporated and the mixture becomes fluffy
Gradually add the all-purpose flour to the butter-sugar mixture. Mix it gently until the dough comes together. It might seem crumbly at first, but continue mixing until it forms a cohesive dough.
Transfer the shortbread dough into the prepared pan, using slightly wet hands to press the dough evenly into the pan to create a smooth surface.
Using a knife or a pastry cutter, score the dough into desired rectangle shapes. Then, using a fork, gently pierce the surface of each rectangle to create small holes or designs.
Place the pan in the preheated oven and bake the shortbread for 30-35 minutes or until the edges turn golden brown.
Once baked, remove the pan from the oven and let it cool for about 10-15 minutes. Using the parchment paper overhang, carefully lift the shortbread out of the pan onto a cutting board. Cut along the scored lines to separate the rectangles while the shortbread is still slightly warm.
Allow the shortbread cookies to cool completely on a wire rack before serving or storing in an airtight container.
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Notes
Store cooled shortbread cookies in an airtight container at room temperature for up to a week. They can also be frozen for longer storage.