In a heavy saucepan, combine sugar and water and stir until the sugar is dissolved. Bring the mixture to a boil and cook until it turn golden. Don't stir, just swirl the pan every now and then. This will take max. 10 minutes. (Note 1)
Add the nuts, lemon zest, butter and salt and mix until coated.
Pour mixture onto the baking sheet and spread with a spoon. Make sure you have 1-layer of nuts.
Cool completely and break into pieces. Store in an airtight container.
Notes
Be aware that once the color starts turning it can quickly go too far.