- Preheat the oven to 170°C, gas 3. Roll out the pastry to a 30cm square
- Melt butter in a frying pan, add the onion and cook gently for 5 - 10 minutes, until softened. Leave to cool.
- Place the sausage mixture down the centre third of the pastry, leaving a border about 4cm empty at the top and bottom, then spoon the onions evenly on top of the sausage meat.
- Cut slits in the pastry from about 3cm away from the sausage mixture to the edges, approx 2 cm wide.
- Fold the top and bottom borders of pastry over the sausagemeat then take pastry strips from alternate sides and lie over the sausage meat to make a plait. Tuck any extra strips underneath.
- Glaze the plait with beaten egg.
- Transfer to a baking tray and cook for 45 - 55 minutes, or until golden brown and cooked through.