Beef

Sift flour and salt into a large mixing bowl
Push the egg yolk through a fine sieve into the flour
Add the egg and mix until combined
Beat in butter 1 tablespoon at a time
Place dough on a floured surface, knead until smooth and elastic, wrap in waxed paper, and refrigerate until firm (at least 30 minutes)
Melt 2 tablespoons butter over medium heat and sauté onion and rutabaga until the onion is soft and transparent (about 5 minutes)
Grind or finely chop the cooked onion, rutabaga, and beef brisket
Melt the remaining 4 tablespoons butter over medium heat and add the meat mixture
Cook over low heat, stirring occasionally, until the liquid evaporates and the mixture holds its shape
Remove from heat, let cool, stir in one beaten egg, and season with salt and pepper
Preheat the oven to 350°F
On a lightly floured surface, roll the dough into a 13x8-inch rectangle (1/8 inch thick)
Spoon the filling down the center lengthwise, leaving about 1 inch at each end
Brush the long sides with cold water and fold one long side over the filling, then fold the other over it
Brush the short ends with cold water and fold them over to enclose the filling
Place the pastry seam side down on a baking sheet and brush the top with the remaining beaten egg
Bake until rich golden brown, about 30 minutes
Slice diagonally into 1.5-inch pieces and serve