Place the 50g Walnuts in a food processor and finely chop, add the Parmesan, flour, thyme and butter and whizz until the mixture comes together, like pastry, and is smooth, stiff and well mixed. Do not be tempted to add extra liquid.

Move the dough onto a floured work surface and form it into two neat cylinders about 4cm in diameter. Wrap in clingfilm and chill until firm, about an hour.

Preheat the oven to 180ºC, gas mark 4.

Put a piece of foil onto the work surface and add the 75g chopped Walnuts. Brush the cylinders with the egg generously all over the sides (not the ends) and roll in the Walnuts, then transfer to a board or plate.

Line 2 large baking sheets with baking parchment. Slice each cylinder into 16 discs and place on baking sheets, well spaced. Bake for 17-18 minutes, swapping the trays over halfway, or until golden. Transfer to a cooling rack to cool completely.