Pickled walnut and cheese rolls

Method

1. Heat the oven to 200°C fan/gas 7 (unless you plan to freeze the rolls for another day). Put the mashed potato, grated cheddar, roughly chopped pickled walnuts and finely chopped banana shallot in a bowl. Season with a pinch of salt and pepper, then mix until evenly combined.
2. Unroll the pastry sheet and cut in half lengthways so you have 2 long pieces. Divide the mixture in half and roll each into a sausage about 2.5cm thick and roughly as long as the pastry. Carefully lift and transfer each sausage to the centre of each piece of pastry. Brush the beaten egg along one edge of the pastry, then roll the pastry around the filling and press the edges together to seal.
3. Use a fork to crimp the edges, then brush the logs all over with egg and sprinkle with nigella seeds. Cut each log into 9-10 rolls and put on a large baking tray lined with baking paper (you can use the paper the pastry came with). Transfer to the freezer or bake for 12 minutes until golden and crisp. If the mixture has spilled out a little, you can gently push it back in with a butter knife and as it cools it will set in shape. Leave to cool to room temperature for the filling to firm up, then enjoy.