Process all mince ingredients except the water in a food processor for about 1 minute to break into smaller pieces, like a crumble.
Placing your puff pastry sheets on a lightly floured bench, form 1 large piece, ensuring the sheets are pressed together firmly. Pour the walnut mince in the middle of the sheets and using your hands form a firm log in the centre, leaving some room at each end to tuck in the pastry sides.
To wrap the pastry, starting with the side closest to you, carefully roll the puff pastry right over the mince and from into a long log, tucking in the pastry ends as you go. Transfer the pastry, fold side down onto an oven tray lined with baking paper. If the pastry comes apart a little, that’s okay, just press the pastry together to cover the gaps.
Using a sharp knife, make large diagonal scores on top of the pastry to help steam escape and for ease of cutting when the pastry is cooked.
Taking a pastry brush, paint the pastry all over with maple syrup. This will create a lovely glaze.