Preheat your oven to 350°F (180°C) and line a cookie sheet with parchment paper. After the dough has chilled, roll it out on a silicone mat or a clean surface. Sprinkle powdered sugar to prevent sticking, not flour. Roll the dough to about ¼ inch thickness.
To shape the kolaczki, overlap opposite corners of the dough square towards the center over the filling, pressing the dough together lightly to seal. Brush a tiny bit of water or beaten egg white on one point to help seal the opposite point on it.