Preheat the oven to 325°F (163°C). Line a 9×13-inch sheet pan with parchment paper, leaving an overhang on the sides for easy removal.
In a large mixing bowl, cream the softened unsalted butter and granulated sugar together using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
Add the vanilla extract and mix until combined.
In a separate bowl, whisk together the all-purpose flour and salt.
Gradually add the flour mixture to the butter mixture, mixing on low speed until just combined. Do not overmix.
Transfer the dough to the prepared sheet pan. Use your hands or a spatula to press the dough evenly into the pan, smoothing the top.
Using a fork, prick the dough evenly all over to prevent bubbling during baking.
Bake in the preheated oven for 30 minutes, or until the edges are lightly golden but the center is still pale.
Remove from the oven and allow the shortbread to cool in the pan for 10 minutes.
Using a sharp knife, score the shortbread into 24 squares while still warm. Let cool completely in the pan before lifting out using the parchment paper.
Once cooled, separate the squares and store as desired.