- Add the sausagemeat, mustard and a generous amount of seasoning to a large bowl then mix together to combine.
- Unroll the sheet of puff pastry onto a lightly floured work surface then roll out slightly thinner to create a large rectangle about 40x30cm. Cut the sheet in half lengthways so that you have two long strips.
- Take half the sausagemeat mixture and form it into a long sausage shape down the centre of one pastry strip, leaving a clear border either side. Repeat with the remaining sausagemeat and pastry.
- Beat together the egg and Marmite in a small bowl then lightly brush over the pastry borders to glaze.
- Fold the pastry over the sausagemeat filling to enclose, pressing the egg-glazed edges together. Use a fork to crimp the pastry together to seal then trim the rough edges with a sharp knife.
- Brush the pastry all over with the remaining egg glaze and sprinkle over the Nigella seeds. Cut each long roll into 6 individual pieces for larger rolls, or 10 smaller ones for canapé-sized rolls.
- Transfer to a baking tray lined with baking paper then chill in the fridge for 20-30 minutes (or up to 1 day if making ahead) to firm up.
- Preheat the oven to 200°C/Fan 180°C/Gas 6. Bake for 15-20 minutes (depending on their size) or until the pastry is crisp and golden and the filling is fully cooked through. Can be served hot or cold as part of a party spread or buffet.
Tips: You can add lots of different flavours to your sausagemeat filling, try chopped sundried tomatoes or olives in summer, crumbled chestnuts and dried cranberries at Christmas, or any chopped herbs you have to hand. Likewise, don’t be put off by the Marmite glaze, it adds a subtle savoury flavour but you can leave it out if you prefer.