Preheat oven to 180C/160C fan-forced. Line 3 baking trays with baking paper.
Using an electric mixer, beat butter, sugar and vanilla until pale and creamy. Add egg. Beat until combined. Sift flour over butter mixture and add 100s and 1000s. Using a wooden spoon, stir to combine.
Place dough on a lightly floured surface. Shape into a 30cm log. Wrap in plastic wrap. Refrigerate for 2 hours or until firm. Remove and discard plastic wrap.
Slice into 1cm-thick rounds. Place on trays. Bake for 12 minutes or until golden. Cool on trays for 5 minutes. Transfer to a wire rack to cool completely. Serve.