In a large bowl, combine flour, brown sugar, salt and baking powder. Cut in shortening, half at a time, until crumbly. Combine 1/2 cup water, egg and vinegar; add all at once to flour mixture and toss with a fork until dough forms a ball. Add remaining water only if necessary. Wrap tightly and refrigerate for several hours.
Meanwhile, combine all filling ingredients. On a lightly floured surface, roll out a fourth of the dough to 1/8-in. thickness. Using a 3-1/2- to 4-in. round cutter, cut dough into circles. Place on ungreased baking sheets.
Spread a scant tablespoon of filling on half of each circle. Moisten edge slightly with water and fold over, sealing with the tines of a fork. Repeat with remaining dough and filling.
In a small bowl, beat egg with water; brush tops of pasties. Sprinkle with poppy or sesame seeds.
Bake at 400° for 15-20 minutes or until golden. Serve warm or cold.