Heat the oven to 325F. Line a 9x9 or a 9x13 pan with parchment paper, leaving some paper overhanging the sides, to life it out later.
In a large mixing bowl, cream together the butter and sugar until it's pale and fluffy. Add the vanilla. stir to combine.
Sift in the the flour and salt. Add the nibs. Stir to combine. The dough will be a bit crumbly, and you don't want to handle it too much. But give it a few presses and kneads, to make sure it's sticking together.
Press the dough firmly into your chosen pan. Try to flatten and even out the top.
Bake for about an hour. The top should look dry and slightly golden. Rotate the pan halfway through as well.
Cool in the pan for about 15 minutes. Then gently remove from the pan using the parchment paper overhang. Once they are just cool enough to touch, cut them using a serrated knife, like a bread knife. I cut them into 4 rows of 8, but cut them to any size you want.
Allow the cut cookies to cool fully on a wire rack. Store in an airtight container for up to 3 weeks. These cookies also freeze really well in a sealed container or bag for about 3 months.