Beat the butter and sugar in a large bowl until pale and fluffy.
Gradually beat in the vanilla extract and the egg until combined.
Sift in the flour, baking powder, and salt, then mix until smooth.
Pour the batter onto a 30cm square of cling film.
Wrap the dough into a 7-8cm wide sausage shape and chill for one hour until firm.
Preheat the oven to 200°C.
Cut the dough into 1cm slices and place them on a baking tray.
Sprinkle with optional toppings if desired.
Bake for 8-10 minutes until the edges are golden-brown.
Cool on the tray for 2 minutes before transferring to a wire rack.