Sift flour and salt into a large mixing bowl.
Use a spoon to push the egg yolk through a fine sieve into the flour.
Add the raw egg and mix well.
Beat in butter 1 tablespoon at a time.
Place dough on a floured surface and knead until smooth and elastic, then wrap in waxed paper and refrigerate until firm (at least 30 minutes).
In a heavy skillet, melt 2 tablespoons butter over medium heat; saute the onion and rutabaga until the onion is soft and transparent (5 minutes).
Put the onions, rutabaga, and beef through a meat grinder twice if you have one, if not just chop them up as fine as possible.
Melt the remaining 4 tablespoons butter over medium heat, and add the meat mixture.
Cook over low heat, stirring occasionally, until all of the liquid has evaporated and the mixture is thick enough to hold its shape.
Remove from heat and let cool, then stir in 1 egg, and season with salt and pepper.
Preheat oven to 350°F.
On a lightly floured surface, roll the dough out into a 13x8" rectangle (1/8" thick).
Spoon the filling down the center of the rectangle lengthwise, leaving about an inch of space on each end.
Lightly brush the long sides with cold water, then fold one of the long sides over the filling and the other side over the top of that.
Brush the short ends with cold water and fold them over the top, enclosing the filling.
Place pastry seam side down on a baking sheet and brush the top evenly with the remaining scrambled egg.
Bake in preheated oven until rich golden brown (30 minutes).
Slice pastry diagonally into 1. 5" long pieces and serve as an appetizer or with soup.
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