Roll lemons under your hand on the kitchen counter to soften. With a microplane or zester, zest the 2 lemons. Cut the lemons in half and juice with a citrus juicer or press and keep to the side.
Sift together flour, baking powder, bicarbonate of soda and yellow colour.
Into a stand mixer fitted with a paddle attachment, cream together butter, caster sugar and light brown sugar on a medium-high speed. Scrape down the bowl every so often until it is light and pale.
Add egg and mix until completely incorporated.
Add in the lemon zest and juice and combine.1
Add the dry ingredients in ⅓ increments and mix in before adding the next portion. Once it is all combined spread flat onto a grease or lined tray and cover into the fridge for 1-2 hours to set firm.
Portion and roll the cookie dough into 20-30g balls and place onto a line tray, straight into the freezer for 30 minutes or fridge for 1 hour. Preheat the oven to 160℃ (320℉).
Grease and line the baking trays with paper, fill icing sugar and caster sugar into separate bowls. Take the dough balls out of the freezer and roll into caster sugar and then icing sugar and onto the baking tray. Repeat for all dough balls.
Reroll all the dough balls in icing sugar a second time coating them generously in icing sugar, back onto the trays leaving plenty of space between each.2 Set the trays in the oven for 9-12 minutes. Leave them too cool on the trays for 10 minutes before transferring them onto a wire rack to cool completely.
