In a stand mixer fitted with a paddle attachment, cream the butter, granulated sugar, powdered sugar, vanilla, and salt by mixing on medium to medium-high speed until thoroughly combined and creamy, about 3 minutes.
1 cup unsalted butter, ¼ cup granulated sugar, ¼ cup powdered sugar, ¼ teaspoon salt, 1 teaspoon vanilla extract
Stop the mixer and scrape the bottom and sides of the bowl. Turn the mixer on low speed and add ⅓ of the flour into the butter mixture. Once the flour looks combined, add another ⅓ of the flour, allow it to combine then add the remaining flour. Scrape down the bottom and sides of the bowl and mix on low one more time to ensure everything is combined.
2 cups all-purpose flour
Spread out a long piece of plastic wrap on a clean counter. Dump the shortbread dough onto the plastic wrap. Gently squeeze the pieces of dough together to form one mass of dough. Wrap the plastic wrap around the dough to prevent the dough from sticking to your hands and gently shape the dough into a smooth log about 2 ½ inches in diameter. Twist the ends of the plastic wrap to seal the log and place in the fridge to chill for at least 30 minutes and up to 1 week. Tip: to keep the log smooth and round while it’s chilling, take an empty cardboard paper towel roll or toilet paper roll, cut it lengthwise on one side and place around the shortbread dough before placing it in the fridge. This will prevent the side of the dough that is down on the shelf from becoming flat. Alternately, form the dough into a square about 2 inches high for rectangular shaped shortbread cookies.
Once cookie dough has chilled, preheat the oven to 325° and line 2 baking sheets with parchment paper.
Remove the cookie dough from the fridge, unwrap the plastic wrap and place on a clean cutting board. Slice the cookie dough into ½-inch thick slices. Place cookie dough about 1 inch apart on the prepared baking sheet. For traditional looking shortbread, use the tines of a fork to dock or poke holes in the top of the cookie dough. This releases steam and prevents the cookies from puffing up too much during baking.
Bake the cookies until just golden at the edges, about 20-22 minutes. The baking time will depend on how thick the cookies are. For thicket cookies you may need more time. Check for doneness by looking for edges that are starting to brown and the tops of the cookies no longer look wet. Remove from the oven and allow to cool completely before serving.