Preheat the oven to 180ºC/160ºC fan, and line a 9x9" square tin with parchment paper.
Add the butter, light brown sugar, and white granulated sugar to a bowl and beat together until creamy. A stand mixer with the beater attachment works best for this task!
Incorporate the egg, vanilla extract, and red food coloring into the mixture, and beat again until everything is well combined.
Gradually add in the plain flour, cocoa powder, bicarbonate of soda, and sea salt. Continue to beat until a smooth cookie dough forms.
Fold in the white chocolate chips until they are evenly distributed throughout the dough.
Press the cookie dough into the lined tin, ensuring it's spread evenly.
Bake the cookie bars in the oven for 18-22 minutes, or until the top looks dry and set.
Once baked, allow them to cool in the tray before cutting them into squares. Enjoy your delicious red velvet cookie bars!