Beat the butter, powdered sugar and flavoring until frothy. Stir in egg and yolk. Mix the flour and cornstarch and sieve onto the egg mixture, also stir in. Pour the dough into a piping bag with a star nozzle and squirt rosettes onto a baking sheet lined with baking paper.
Bake in the preheated oven at 180 ° C for about 15 minutes. Take out of the oven and let cool down.
Note: Since the dough is very soft, it is not suitable for processing with the pastry press. But when I wanted to use the pastry press, I just added a little more flour to the dough to make it a little firmer.