No need to preheat the oven yet as this dough needs to chill. Place the sugar, butter and lemon zest into a large bowl, or the bowl of your stand mixer and beat on medium-high speed until light and fluffy. Around 2 minutes.
Add in the egg and egg yolk and mix until well incorporated. Add in the yellow food colouring and mix until the colour is evenly dispersed, I did 3 drops of Wilton gel colour. If you're not happy with the shade after you've added the flour, you can always add more.
Add in the lemon juice and mix until well combined.
Place the flour, cornflour, bicarbonate of soda, baking powder and salt into a medium sized bowl and briefly stir to combine. Tip the flour mixture into your egg mix and beat on low speed until the dough starts to come together. Once the dough comes together, turn the speed up to medium and mix until you have one big lump of dough. If the colour isn't the right shade of yellow for you, add a bit more.
Place your dough into the bowl you mixed the flour in and cover with cling film. Place in the fridge for 2 hours.
Once the dough has chilled, preheat the oven to 180C/350F and line 2 baking trays with grease proof paper/a slicione mat.
Place your icing sugar into a shallow bowl. Take a 1.5tbsp cookie scoop and scoop the dough into balls. Roll the dough balls in icing sugar and then place 2 inches apart on your baking tray. Repeat until you've used all the dough. I made 22 cookies from this dough. There's no need to flatten the dough balls at all.
Place the cookies in the oven for 11-13 minutes. 11 minutes for an extra chewy and buttery cookie, 13 for a slightly more cakey, chewy cookie.
Leave the cookies to cool on the baking tray completely, before storing in an airtight container. Lemon Crinkle Cookies will keep at room temperature, for 5 days.