Make Hamentaschen Honey Dough. Roll into a ⅛-inch layer large enough to cover bottom and go up sides of pan; trim off all but ⅜ inch that hangs beyond edge of pan. (You can use a 13×9 or 9×9 pan, depending on how much you want to make.) Spread a layer of filling on the bottom. Roll a layer of dough, a bit thinner than the outside layer. It needs to be big enough to cover the bottom and just fit in side the pan without going up the sides (or just a bit).
Alternate layers of filling and dough, ending when the last layer is near the top of the pan. You want to use many different kinds of fillings, such as Poppy Seed Filling, Prune Filling, preserves, chopped nuts, chocolate bits, etc. Commercial pastry filling should give you a broad range of choices.
When you get to the last layer, fold outer layer that you first placed in the pan back over the top layer of dough and try to seal it. Brush top with a beaten egg, sprinkle generously with cinnamon sugar. Bake in oven at 325 F convection for 45-50 minutes. It will be a fairly dark brown on top.
Let cool and store covered. Cut into small squares. Fluden can also be frozen in chunks.