Grease a cookie mold with baking spray or line a cookie sheet with baking paper.
Beat the butter, lemon zest, and brown sugar together using a mixer fitted with the paddle attachment until light and fluffy (at least 3 minutes).
In a separate bowl, sift the flour and salt together.
Add the flour mixture to the butter and mix on low speed until blended.
Using floured hands, press the mixture into the prepared cookie mold or transfer the dough onto a floured surface, divide it into two and shape each section into a cylinder. Wrap in plastic wrap and chill until firm.
Remove dough from the refrigerator, cut it into half-inch slices, and place them on a lined cookie sheet an inch apart.
Bake for about 10 to 12 minutes, rotating the baking sheet halfway through the baking time.
Transfer to a cooling rack to cool in the pan.
Notes
Use room temperature softened butter – Butter that’s too firm won’t incorporate well into the sugar, which is key to tender shortbread.
Beat your butter and sugar together well – a good 3 to 4 minutes will give the best results. You can’t overmix at this stage, so beat it another minute if in doubt.
For the lightest lighter texture, don’t skip sifting the dry ingredients before adding them to the butter and sugar.
Flour your hands before working with the dough to keep it from sticking.