Preheat the oven to 350°F (175°C or 165°C for fan ovens).
Line two baking sheets with baking parchment. (You will need to bake the cookies in batches.)
Sift the flour, baking powder and salt into a medium bowl. Set aside.
Cream the butter and 1 cup sugar together in an electric mixer until light and fluffy.
Beat in the beaten egg and egg yolk along with the lemon rind.
With the mixer on medium speed, add the lemon extract and lemon juice.
Lower the speed on the mixer again and gradually add the flour mixture, blending the mixture well. Do not beat.
Pop the dough in the refrigerator for ten minutes to make it easier to form balls. (If you are impatient like I am, you can do this straight away. It's just easier if you chill the dough a bit first!)
Pour the ½ cup sugar into a bowl or on to a plate with raised edges.
Roll the chilled dough into balls about 1 inch in circumference between the palms of your hands. Don't panic, you don't have to measure them, just be sure they are all roughly the same size. It's tempting to make them bigger but as these cookies spread it really isn't a great idea to do that!
Roll each cookie ball and sugar and place on the baking sheets about two inches apart.
Bake for 10 to 12 minutes, watching the cookies carefully so they don't brown too much.
Remove from the oven and allow to cool on the baking sheets for five minutes before carefully removing them with a spatula and cooling completely on a wire rack.
Use fresh baking parchment for each batch.
When cool, store in sealed container at room temperature.