Preheat oven to 275°F (135°C).

Butter a 9x13 inch baking pan and line with parchment paper.

In a mixer, cream butter and sugar until light and fluffy (about 2 minutes).

Add salt and vanilla extract and mix until combined.

Gradually add flour, mixing on low speed until just combined.

Press the dough into the prepared pan, ensuring an even and smooth top.

Cut the dough lengthwise into nine strips.

Cut the strips crosswise into thirty-six 3-inch bars.

Create a decorative pattern on the surface using a fork or skewer.

Bake for 70-85 minutes, or until pale golden.

Transfer the pan to a wire rack to cool completely.

Invert the pan to remove the shortbread and parchment paper.

Turn shortbread over, break or cut into bars.

Store in an airtight container.