Preheat the oven to 180°C/160°C fan oven/Gas Mark 4.Whiz the flour, salt, caster sugar and 125 g (4 1/2 oz) of the butter in a food processor until it begins to come together. Press the mixture into a 20 x 30cm (8 x 12 in) greased Swiss roll tin and smooth over with the back of a spoon. Bake for 20 to 30 minutes or until golden. Leave to cool.

Put the remaining butter, muscovado sugar, syrup and condensed milk in a pan and heat gently, but do not boil. Whisk together until combined. Pour over the shortbread, smooth the surface and chill for 3 hours.

Melt the chocolate in a heatproof bowl over a pan of simmering water. Mix with the nuts and pour over the fudge mixture. Smooth the top and leave to set. Cut into wedges to serve.