In a medium bowl, stir together the flour, baking powder and salt; set aside. In a large bowl, whisk the oil, eggs, egg yolk, sugar, zest, both juices and brandy until smooth. Gradually stir in the flour mixture until a sticky dough is formed. Wrap in plastic wrap, flatten into a disk and chill overnight.
When ready to bake, preheat oven to 375 degrees F.
Working with about one quarter of the dough at a time and leaving the remaining in the refrigerator, roll on lightly floured surface a little less than 1/4-inch thick. Cut circles (or other fun shapes) using cookie cutters 2 1/2 to 3 inches. Place a spoonful of filling in center (about 1 teaspoon per cookie) and then pinch one side up. Turn and pinch second and then third to make a triangular shape. Leave a little bit of the filling showing at the top. For non-traditional shapes, use your imagination: tubular, squares, bite-size or even some flat cookies depressed in the center with a bit of filling there.
Place cookies on parchment paper on cookie sheet, brush with a little beaten egg for sheen and bake until nicely browned, 10 to 15 minutes.
Keep room temp in airtight container but consume within 3 to 4 days, tops.
Combine everything except the lemon zest and juice and the beaten egg into a saucepan and cook over moderate heat until thick, 10 to 15 minutes. Stir often. Add zest and juice. Take a bit of the filling and mix it into the beaten egg. Repeat, then mix the egg mixture into the pot of filling. Cool overnight.
Other types of fillings may be used such as apricot, raspberry, prune mixed with chopped nuts, etc. Personally, I'm going to use some Robertson's English Mincemeat in my next batch and drizzle with rum or hard sauce. Not traditional, but might be a fun way to introduce them to non-Jews. *Poppy seeds go rancid quickly after opening.