Mix margarine, cottage cheese, flour, salt, and sugar in a larger mixing bowl.
Let dough sit covered overnight in the refrigerator to chill.
Roll out dough as thinly as possible with a rolling pin. Sprinkle flour on the rolling surface and rolling pin so the dough does not stick to them.
Score into squares (about 3 inch squares).
Place a “blob” of filling in the middle of each square (about a ½ tablespoon).
Fold the diagonal corners of the square inwards toward one another - slightly overlapping the edge.
Using lightly beaten egg whites as a “glue,” dip your fingers in the egg whites and press/pinch the overlapping corners together.
Place on baking sheets (use parchment paper if not non-stick).
Bake at 350 degrees for 10-15 min, until the tops are golden brown.
Remove from the oven, and move from cookie sheets to a cooling rack. Sprinkle with powdered sugar.
Store in an airtight container.