250g unsalted butter, chopped, at room temperature
¾ cup caster sugar
3 teaspoons unicorn flavour for icing
2 ½ cups plain flour
Blue, purple and pink food colouring
Extra plain flour, for kneading
½ cup hundreds and thousands
Grease two large oven trays and line with baking paper.
Beat butter, sugar and flavouring in small bowl of an electric mixer until pale and creamy. Beat in egg, until combined.
Stir in flour, in two batches, to form a soft dough. Divide evenly between three bowls. Tint each portion with a different food colouring. Knead one portion at a time on a lightly floured surface until smooth and no longer sticky.
Roll out each portion, separately, between two sheets of baking paper into a 20cm x 25cm rectangle. Remove top sheets of baking paper from each rectangle.
Invert blue dough over pink dough, remove top sheet of paper, then invert purple dough over the blue dough, leaving top sheet of paper in place.
Roll out the layered dough into a 30cm x 35cm rectangle. Remove paper from top. Using the bottom sheet of paper as a guide, roll up dough firmly from the long side to form a log-shape.
Sprinkle hundreds and thousand down the length of the log on the paper. Roll the log to coat evenly. Wrap in baking paper. Refrigerate for 45 minutes, or until firm.
Unwrap log. Cut into 1 ½cm-thick slices. Place about 4cm apart, on prepared trays.
Cook in a moderately slow oven (160C) for about 15 to 18 minutes or until cookies are just firm when lightly touched. Remove. Stand on trays for 10 minutes before transferring to a wire rack to cool.