Instructions

1. Preheat oven to 180 C (350 F) standard / 160 C (320 F) fan-forced. Grease and line an 8-inch square pan with baking paper, ensuring two sides overhang.
2. In a large mixing bowl, beat butter and sugar with an electric mixer until pale and creamy. Add vanilla and egg and beat again. Sift in flour and baking soda and stir until a soft cookie dough forms.
3. Add the chocolate chips and sprinkles. Transfer the cookie dough to your tin and spread out gently to form one even layer. Bake for approximately 18-20 minutes or until golden brown. Leave to cool completely.
4. To make the unicorn buttercream, beat the butter and vanilla until pale and creamy. Add the icing sugar, one cup at a time, along with the milk, until thick and smooth. Divide the buttercream into two bowls and add a tiny bit of food gel into each one. I used a Teal food gel for the turquoise and a Violet food gel for the purple.
5. Place both frostings into a large disposable piping bag fitted with a large round tip. Pipe swirls of buttercream over your cookie slice, then scatter over extra sprinkles. Cut into bars and serve.