Line two baking trays with greaseproof paper/baking parchment and set aside.
In a large mixing bowl, cream together the butter and sugars until light and fluffy.
Add the egg and blue food colouring or blue spirulina and beat in. You can add more blue food colouring later if needed.
Sieve in the flour, then spoon in the baking powder, bicarbonate of soda, salt and the cornflour (if using) and mix in until a dough is achieved.
Add more blue food colouring here if needed and gently knead it in. Avoid overworking the dough as much as possible.
Press in the chocolate chips.
Shape your dough into up to 12 equal balls. Sit them on the trays with 6 on each tray, leaving a generous amount of space in between each ball.
Chill the cookie dough pieces in the fridge for at least 1 hour or in the freezer for 30 minutes. Do not skip this step as you could end up with flat cookies!
After about 50 minutes of chilling, preheat the oven to 200°C [390°F] or 180°C fan.
When ready, bake the cookies for around 8 to 10 minutes, until slightly dry looking on the top. They shouldn’t need pressing down before baking as they may spread too much, but this personal preference. Do not bake for longer than the allotted time: they will continue baking on the trays after.
After the allotted time, leave the cookies to continue baking on their trays for at least 30 minutes.
Spray with the glitter if using. Then your blue chocolate chip cookies are ready to eat!