Mix in flour and baking powder. Add hazelnuts. Roll on floured board into two logs. (Mixture can be a bit dry so add small amounts of water to get it to stay together. It should still be quite dry though. )
Slightly flatten the logs onto greased (or non-stick) baking tray or baking paper. Bake for 40-45 minutes.
Remove from oven and cool. Cut into 1 cm thick slices. Logs are easier to cut if they are not cooked too much at this stage.
Lay slices on their side and cook for 15-20 minutes. Turn once during this time.