Beat the butter, sugar, salt and vanilla together until smooth and creamy.

Mix in the egg yolk until well incorporated, scraping down the sides of the bowl at least once.

Add the flour and mix just until incorporated.

Scrape onto a lightly floured board and knead a few times, just until the dough smooths out.

Turn onto a sheet of plastic wrap and roll into a log, wrap up and refrigerate for several hours or freeze.

Before baking, preheat the oven to 325°F.

Line your baking sheets with parchment.

Slice the dough into slices about 1/8" thick and place them on the sheets about an inch apart (they won't be spreading very much, but they need air room around each cookie).

Bake until JUST beginning to turn golden around the edges, about 16-18 minutes.

Note: you can do many things with these cookies.

You could roll the dough out and cut shapes.

You could slice them even thinner and sandwich them with chocolate or jam or lemon curd.

You could make them and then dip them half into chocolate.

You could just make them and eat them, which is my favorite.

Whatever you do, they will be delicious.