In a large mixing bowl, beat together the butter and sugar until fluffy, or mix in a stand mixer fitted with a paddle attachment.
Add the lemon zest and juice and beat until just combined.
Add the flour and salt (if using) and mix until all the flour is incorporated. Gather the dough so everything comes together to form a ball.
Place the dough on a piece of parchment paper. Cover with another piece of parchment paper. Roll out to about ¼ inch thick. Place the dough together with the parchment paper on a baking sheet and place in the fridge to chill for one hour.
As the dough chills, preheat oven to 350° Fahrenheit or 180° Celsius.
Take out the dough from the fridge, remove the top parchment paper, and cut the dough out into 2-inch circles using a 2-inch cookie cutter. You could also cut the dough out into different shapes with different cookie cutters. Re-roll the scraps of the dough and cut out more cookies.
Place the cookies on an 11 by 13 inch baking sheet lined with parchment paper. (Cover again with parchment paper, roll out and keep any leftover cookie dough in the fridge until ready to bake.) Bake in the preheated oven for about 13-15 minutes until the cookies are slightly brown around the edges and slightly firm to the touch.
Let the cookies cool on the baking sheet for 5 minutes. Then transfer them to a cooling rack and let them cool completely.
Cut out and bake the remaining cookie dough.
Serve with milk, hot tea, or coffee.
Notes
1. Storage: Store lemon shortbread cookies in an airtight container or Ziploc bag for up to 7 days.2. No cookie cutter? Roll the dough into a 2-inch round log. Let it chill for about 2 hours or until the dough is firm. Then using a knife, cut the dough into 1-inch thick round cookies.3. Lemon glaze: Make a lemon glaze with lemon juice and powdered sugar then drizzle the glaze over the cooled cookies.4. More sweetness: Sprinkle granulated sugar over the cookies before baking for more sweetness and some texture.