Combine flour and powdered sugar in a large bowl or mixing dish. Cut the butter into smaller pieces and add it to the flour mixture. Crumble the butter into the flour mixture until the butter is finely divided and resembles grated Parmesan cheese. Gather the dough with the egg.  Knead all ingredients together into a uniform dough. Knead as briefly as possible, stopping when the dough comes together. Divide the dough into 4 equal parts. Roll each part into a log and flatten them (about 1 cm thick). Whisk the egg with a fork in a deep plate. Brush the dough logs with the beaten egg and sprinkle with coconut flakes. Place them in the refrigerator and let them get completely cold.  Then cut them into pieces about 1 1/2 centimeters in size. Place the cookies on baking sheets lined with parchment paper. Bake the cookies for 6-8 minutes at 200 degrees Celsius (392 degrees Fahrenheit) in a regular oven (180 degrees Celsius (356 degrees Fahrenheit) for a fan oven). Let the baked cookies cool on a cooling rack.