Preheat the oven to 175°C (340°F/Gas 4). Line a large baking tray with baking paper. Stir the salt into the flour. Beat two-thirds of the beaten eggs in a bowl using a hand blender (you will need the reserved one-third later to spread on the biscuits). While stirring, add the sugar and vanilla sugar as well as the lemon juice and oil. Sift the flour over a bowl and stir. Add the milk, add a little more if it appears necessary. Lastly, quickly knead in the chopped nuts. Cut the dough in half, and roll both halves into two equal ‘ropes’. Slightly separate them on the baking tray and coat them with the reserved egg. Bake the biscuit ropes for 25–30 minutes or until golden brown. Leave to slightly cool on a rack and cut each into 12 equal slices with a sharp knife. Return to the baking tray and bake for a further 10 minutes on each side until golden brown. Leave to fully cool on a rack.