In a bowl, mix flour with the baking powder. Add sugar, vanilla sugar, salt and almond essence and mix well. In the centre, make a hollow and add the butter and eggs. Work everything into a dough. Finally, knead in the almonds and form it into a ball with a bit of flour. Chill for 30 minutes in the fridge.
Cut dough into 6 pieces and form each piece into a 25cm long log.
Preheat oven to 200 C / Gas 6. Line a baking tray with baking parchment.
Place logs 8cm apart and bake for 10-15 minutes. Allow the rolls to cool and cut diagonally into 1cm thick slices. Lay on the baking tray and bake for a further 8-10 minutes at 200 C / Gas 6. The biscotti should be golden.
Allow to cool completely and store in a airtight tin.