Rub 125g of cold butter and 125g of lard into 500g of all-purpose flour with a pinch of salt until crumbly. Mix in 6 tablespoons of cold water to make a firm dough. Cut into four and chill for 20 minutes.
Mix 350g of finely chopped skirt steak, 1 large finely chopped onion, 2 medium peeled, thinly sliced potatoes, 175g of peeled, finely diced rutabaga, 1 tablespoon of ground black pepper, and 1 teaspoon of salt.
Preheat the oven to 425°F / 220°C. Roll each piece of pastry into a 9in / 23cm round, trimming around a plate. Pack a quarter of the filling along the center, leaving a margin at each end.
Brush the edges with 1 beaten egg, draw the sides up to meet on top, and pinch to seal. Place on a nonstick baking sheet and brush with the remaining egg.
Bake for 10 minutes, then reduce the oven to 350°F / 180°C and bake for 45 minutes more, until golden.
