Knead all ingredients briskly in a mixing bowl or on a work surface to form a shortcrust pastry. Let rest in refrigerator, covered with plastic wrap, for 2 to 3 hours before working. Roll out on a floured work surface or between two baking mats to a thickness of 2 to 3 mm. Sweep off excess flour with a flour whisk or brush. Mix egg with salt, dilute with a little milk and brush dough with it. Sprinkle with cheese mixture and freeze until dough is firm to the touch. Using a pastry wheel, cut sticks 2 cm wide and about 12 cm long. Place on prepared baking sheet and bake in preheated oven at 165 to 175 °C for 12 to 15 minutes until golden brown on sight.