Cream light butter, powdered sugar and vanilla sugar in a baking bowl. Fold in eggs. Mix flour and almond kernels and stir spoonful by spoonful with the liqueur into the fat-sugar-egg mixture. Fill batter into a piping bag or possibly a pastry syringe. On a baking sheet lined with parchment paper, pipe dough strips in half circles.
Garnish pastry sheets with almond slivers. Bake the cookies in a heated oven at 180 °C for about 12 minutes.
Tip: Biscuits taste very good fresh. When cooled in a tin and stored in the dark, they become nice and soft and keep just as long.