Place butter, lard, flour and a pinch of salt in food processor, then add 6 tbsp cold water to and make a firm dough. Cut into 1/4’s and chill for 20 minutes.
Preheat oven to 200c.
In a pot heat oil and saute onion, rosemary, celery, swede, and potato until tender. Add peas and season well. Take off heat and cool completely.
Meanwhile, take out pastry and roll on a lightly floured surface until approx. 1/2 cm thin. Using a molding cutter, cut out 8-10 cm discs.
In the center of each disc place a couple of tbsps of potato mix, take egg and brush edges, draw together both sides to the top and pinch edge together to seal.
Transfer on a lined baking tray and brush all over with egg.
Bake for 10 minutes, then reduce heat to 180c and cook for a further 10-15 minutes, until golden brown and crisp.