These classic shortbread cookies are made with just 5 ingredients! They are simple as can be but so buttery and delicious!
Place the sugar and salt in the bowl of a food processor, and process on high until the mixture is milled to a powder (about 1 minute).
Pulse in the butter and vanilla until the mixture looks like coarse breadcrumbs.
Pulse in the flour until the mixture begins to clump up.*
Wrap the dough tightly in plastic wrap and chill in the refrigerator for at least 30 minutes.
Unwrap the dough, trim off any uneven edges, and cut into 3-inch long by 1-inch wide bars.
Dock the cookies with a fork, toothpick, or bamboo skewer, and place them on a parchment-lined baking sheet.
Sprinkle them with additional sugar, and chill in the refrigerator for another 30 minutes.
Preheat the oven to 350 degrees F.
Bake the cookies for 20 to 25 minutes, or until just barely beginning to turn golden around the edges.
If the cookies have spread during baking, they can be trimmed back into shape with a sharp knife while hot from the oven.
*The mixture will seem very crumbly, but it should hold its shape when squeezed. If it is too dry, add 1 to 2 teaspoons of heavy cream to moisten it up slightly, but be very careful not to overdo it as it will cause your cookies to spread in the oven.