In a large nonstick pot, sauté onion in oil until golden. Add meat. Sprinkle with salt and sear on all sides until browned.

Add apple juice and wine and bring to a boil. Lower heat and simmer, covered, for three and 1/4 hours.

Remove meat to a cutting board and allow to rest 10 minutes.

Meanwhile, strain onions from gravy; reserve for sauce. (Set aside remaining gravy for another use.)

Using two forks, pull the veal into strands so it shreds. Set aside.

Place sauce ingredients into the pot that was used to cook the veal (no need to clean it first). Bring to a boil, stirring, then remove from heat. Return pulled veal to pot and combine sauce with meat; allow to cool.

Since this is a large recipe, I recommend dividing the ingredients in half and preparing it in two batches, since your food processor may not be able to process the full recipe at once. Place one and 1/2 cups of flour, 1/4 teaspoon sugar, and 1/4 teaspoon salt into a food processor fitted with the S blade. Process for a few seconds to combine.

Add 1/2 cup (one stick) plus one tablespoon margarine and process until small crumbs form. Add four tablespoons ice water and process until dough begins to come together, adding a little more water if needed.

Remove ball of dough from processor and form into a flat disc. Wrap in plastic wrap and refrigerate for at least one hour or up to two days. Repeat with the remaining dough ingredients.

When ready to prepare hamantasch galette, preheat oven to 350 degrees Fahrenheit (175 degrees Celsius). Remove dough from refrigerator and allow to sit at room temperature for 10 minutes.

Working with half the dough at a time, flour your work surface and roll out dough into a 12-inch (30-centimeter) circle. Place half the pulled veal mixture into the middle of the circle, mounding up some of the filling in the center, and begin to fold up dough into a hamantasch; fold in one side on an angle, then the other side, and then the bottom up, forming a triangle. Make sure to press pointed ends tightly together to avoid leakage. (I ruffled the inside triangle edges to form a more authentic galette look.) Carefully transfer to a Gefen Parchment-lined baking sheet.

Repeat with remaining dough and filling. Brush dough with beaten egg if desired and bake for 45 minutes. Remove from oven and serve hot or warm.