Preheat the Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.

Mix Dry Ingredients: In a medium bowl, whisk together the flour, powdered sugar, cornstarch, and salt.

Cream Butter and Flavoring: In a large bowl, beat the softened butter, lemon zest, and vanilla extract until light and fluffy, about 2-3 minutes.

Combine the Mixture: Gradually add the dry ingredients to the butter mixture, mixing until just combined. If desired, add the fresh lemon juice for a more intense lemon flavor and mix until incorporated.

Shape the Cookies: Roll the dough into 1-inch balls or, for a more traditional shortbread shape, roll it out and use cookie cutters to form rounds or any desired shape. If the dough is too soft to handle, chill it in the fridge for about 20 minutes before shaping.

Bake the Cookies: Place the dough balls or cut-out shapes on the prepared baking sheet. Flatten slightly with the back of a spoon or your fingers. Bake for 12-15 minutes, or until the edges are lightly golden.

Cool: Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.