Place the sugar in a thick bottomed pot with the water and lemon on medium heat.
Swirl a little to spread the water to start, and make sure all the sugar crystals are covered with the water as the pot heats.
Cook until starting to colour around the edges. Swirl the pot to stop the sugar burning in spots and to gather up any unmelted sugar crystals, 6-8 minutes, dont stir the pot. It may look quite crystally at this stage but this should pass.
Watch it carefully and when it is golden add the nuts
Pour quickly onto the prepared tray ( it sets very fast) and push out a bit with the edge of your pot to spread. DO NOT TOUCH IT. Using a fork or spoon could help but they will start to get sticky and make a mess. it is easier to pick up the tray and tilt back and forth to help the liquid sugar spread.
Let it cool completely before breaking into shards or whizzing to a powder in the food processor