Sift the flour and sugar together. Work in the butter, cream cheese and egg. Knead together. An easy way to do this is to put the dough inside a plastic bag - much less messy! Let the dough stand in the refrigerator overnight. About a half hour before you're ready to start making the cookies, put the dough into the freezer. For the filling, mix all of the above ingredients together. You can also used canned poppy seed filling (Solo brand) or an apricot or prune filling. Spread flour and powdered sugar onto the surface where you will be rolling the dough. Roll the dough out thin. Cut into squares about 2 inches on each side. It's easiest to cut if you use a pizza cutter. Spread a small amount of filling (½ to 1 tsp) from one corner to the opposite corner. Don't fill them too much, or the filling will spill out when it is cooking. Fold the two remaining corners to the center, partially covering the filling. Wet your fingertip in a small bowl of water, and seal the edge, or it may open up during the cooking. Bake in a 375℉ (190℃) F oven for about 13 minutes.