Cream the butter and sugar in a stand mixer fitted with the paddle attachement on low speed until combined, then increase the speed to medium and mix for about 2 minutes until fluffy (or use a regular mixer). Scrape down the sides of the bowl as needed.

Add the flour and salt, and beat on low speed until just incorporated, scraping down the sides of the bowl as needed. Add the egg yolk and vanilla and beat on medium low until combined. The dough will be moist and clumpy and should hold together. If it appears dry, add a tablespoon or so of cold water and mix until combined.

Pour the dough out onto a Silpat baking mat or work surface and shape it into a disc. At this point you can wrap it tightly with plastic wrap and store it in the refrigerator for 1-2 days or freeze it.

Tear the dough into chunks and spread across the bottom of a non stick 9 – 9 1/2" tart pan with removable bottom. Press the dough into the edges, then evenly across the bottom of the pan. Cover with plastic wrap and store in the refrigerator for up to 1 day, or bake at 350 degrees for 20 minutes or until lightly golden and it smells like shortbread. For best results, begin checking for doneness after 15 minutes as all oven temperatures vary.

Cool the crust completely, then fill with pastry cream, lemon curd or your favorite fillings. Enjoy!