Beat the butter until frothy. Add sugar and vanilla sugar. Mix in the eggs and yolks. Carefully mix in the flour and cornstarch. Process everything into a smooth shortcrust pastry.
Pour the dough into a piping bag and sprinkle small wreaths on a prepared baking sheet. Bake for about 10 minutes at 190 degrees.
After cooling, spread one wreath with jam and glue together with a second wreath.