Place butter and sugar in the bowl of an electric mixer and beat until pale and creamy.
Add vanilla extract and egg yolks and beat to combine.
Beat in flour and baking powder, then cream, to make a smooth dough.
Wrap dough in clingwrap and chill for 30 minutes in the refrigerator, or until firm.
Flavour one batch of dough as you please, e.g. with chopped honeycomb ('Crunchie' type) by working flavouring into dough.
You can also use any shape you like.
For round biscuits, roll dough into logs about 20 cm long and 5 cm in diameter.
Cut into 4 mm thick slices, place on a greased baking sheet and bake at 180 °C for 15 to 18 minutes.
Cool on a cake rack.
Or, roll out dough to 3 mm thick and cut out shapes with Christmas-design cookie cutters.
Bake and cool, then decorate to taste.
Alternatively, cut out shapes with a large star cutter, then use a small star cutter to cut out centres from half the big stars.
Spread a little jam (strawberry is best) on stars left whole and top with cut-out stars.
Bake, cool and dist with icing sugar.
Bake cut-out stars as mini biscuits.
Work 25 g cocoa powder and 150 g mixed white and dark choclate chunks into cookie dough.
Roll out to 3 mm thick and cut out shapes with a heart-shaped cookie cutter.
Bake, cool and sandwich together with melted chocolate.