Mix all ingredients for the shortcrust pastry with a dough hook in a bowl or on a floured work surface. Cover with plastic wrap and let rest in the refrigerator for 2 to 3 hours. Roll out shortcrust pastry on floured work surface or between two baking mats, not too thin. Cut out any shapes, place on prepared baking sheet and brush with diluted egg if desired. Place one or two Smarties in the center of the cookies and press down a little. Bake in the preheated oven at 165 to 175 °C for about 10 minutes until light brown on sight. My little granddaughter Katharina gave me the idea for the Smarties when we were processing the dough for a photo shoot. She pressed the Smarties into the dough with great care.