1.Preheat oven to 180°C (160°C fan-forced). Grease three oven trays; line with baking paper.
2.Beat butter and caster sugar in a medium bowl with an electric mixer until smooth and pale. Add vanilla, egg and lemon; beat until well combined.
3.Stir in sifted combined flour, hazelnut and cinnamon until a soft dough forms. Shape into a disc, wrap in plastic wrap; refrigerate 30 minutes.
4.Shape 2 tablespoons of dough into a 30cm (12-inch) length. Fold in half and twist together, leaving about 2cm (¾-inch) untwisted at ends. Repeat with remaining dough. Place on oven trays; brush with combined lightly beaten egg white and the water. Sprinkle with demerara sugar.
5.Bake 25 minutes or until golden; cool on trays.
6.Sift icing sugar into a small bowl, add juice and the extra water; stir to form a thin icing. Transfer to a small jug (this gives greater depth when dipping); dip bottom part of twists in icing, place on a baking-paper-lined tray; stand until set.