Beat butter, sugar and egg in a small bowl with an electric mixer until combined. Stir in sifted dry ingredient, in two batches.
Knead dough on a floured surface until smooth. Roll dough between sheets of baking paper until 5 mm thick. Cover and refrigerate for 30 minutes.
Preheat oven to 180c or 160 fan forced. Grease oven trays and line with baking paper.
Using 3 cm, 5 cm and 6.5 cm round cutters, cut 14 rounds from dough using each cutter. Place 3 cm rounds on one oven tray and place remainder on the other trays.
Bake the small cookies for about 10 minutes and the larger cookies for 12 minutes. Cool on wire racks.
Spread tops of cookies with chocolate and sprinkle with hundreds and thousands. Allow to set at room temperature.