Combine lemon zest and sugar in a bowl, rubbing together until fragrant.
Cream butter and lemon-sugar mixture until fluffy using a mixer.
Mix in egg until smooth.
Add lemon juice and lemon extract, mixing gently until combined.
On low speed, gradually incorporate flour until dough forms.
Make a log, wrap in plastic, and chill for 40 minutes in the freezer or at least 4–5 hours in the fridge.
Preheat oven to 170°C / 340°F and line baking sheets with parchment paper.
Slice dough into 5 mm / ⅕-inch thick cookies, place on prepared baking sheets.
Bake for 10 to 12 minutes, until edges just begin to change color. Cool cookies on baking sheets for 5 minutes, then transfer to wire racks to cool completely.