With an electric whisk cream together the butter and sugar. Add the vanilla extract and egg and beat until well combined.
Sift in the flour and beat until it starts to come together. Pour mixture out onto a clean work top and use your hands to bring it together. Give a slight knead before rolling it out to 6mm thick.
For the giant party rings, use a small/medium bowl, around 5 inches wide, as a template. Transfer the giant cut outs onto a baking tray lined with baking paper. Use a small cookie cutter, around 1½ inches wide, to cut a hole out of the centre, this will be used to make the mini party rings. Place the mini biscuit onto the baking tray and use the back of a piping nozzle to cut the centre out.
Repeat with the remaining dough until you have all of your giant and mini party rings. I only re-roll the dough once. Place the biscuits in the fridge to chill while preheating the oven to 180C. Place chilled biscuits in the oven for 15-20 minutes or until golden around the edges.
To create the unicorn horns, take a small amount of fondant. Divide it in two and roll both into a sausage shape. Twist the two together to form the horn. Finish by painting on the gold dust before leaving to harden.
Add water to the Royal Icing Sugar and beat until the icing is runny but thick enough to stay on the biscuits.
Transfer to a plate, colour with food gel and mix. Dip the top of each biscuit into the icing and leave on a baking tray to set. Push the unicorn horns into the icing before it has set, so they can set together. I like to decorate the mini rings with icing and sprinkles.
When the giant party rings have set use a black writing pen to draw the eyes.
To create the unicorn mane pipe rosettes using thicker Royal Icing coloured with gel food colour.