Cream the butter and sugar in a stand mixer on medium speed until light and fluffy (about 4 minutes).

Add lemon zest, egg yolk and lemon juice and mix well on medium speed until everything is smooth and incorporated.

In a separate bowl, sift together the flour, cornstarch, and salt.

Add dry ingredients to the butter mixture in two batches and stir until just incorporated. The dough will be very, very sticky.

Spread half the dough onto a sheet of wax paper, then shape and roll into a 1.5 inch (3.8 cm) diameter log. Repeat with the other half. Twist and tape the ends to seal. (You could use plastic wrap instead of wax paper).

Place each dough log into a cardboard paper towel tube that has been sliced open lengthwise. Alternatively, make a tube out of stiff paper. This is to keep the dough log round while it chills in the fridge.

Chill dough for at least 1 hour in the fridge. I prefer to chill the dough overnight. If you’re in a rush, freezing the dough for about 15 or 20 minutes would also work.

Preheat oven to 350°F (177°C). Line cookie sheets with parchment paper.

The chilled dough will be nice and firm. Unwrap it and slice it into 1/4 inch (0.6 cm) thick rounds. Place onto the prepared cookie sheets.

Bake for 12 minutes, rotating sheets halfway through the baking time. The edges should just be starting to lightly brown. The tops should not be brown.

Cool on sheets for about 5 minutes before removing.

If desired, combine the glaze ingredients until smooth and spread over each cooled cookie with the back of a spoon. Allow to set. Store cookies at room temperature in an airtight container.