Heat the oven to 220°C (200°C fan/425°F/gas mark 7). Cut out a 38cm x 38cm (15in x 15in) square of greaseproof paper and push it into a 20cm (8in) Springform cake tin (pan), flattening it against the sides and pressing it down and over the top edge.
Put the nuts and melted butter in a food processor, add the syrup and salt, then pulse to a coarse crumb - don’t