My family's favorite cookies. Easy to prepare and bake. Always use matured cheese like Edam or Gouda for best result. For crunchier cookies, add some grated parmesan cheese to the dough, and sprinkle some grated cheddar on top for garnish.
Preheat oven to 140 degrees C (300 F). Prepare greased cookie trays. Cut the cold butter into small cubes.
With pastry cutter or two knives, mix the butter, flour and salt (if using) until mixture resembles fine crumbs. Knead in the yolks, and then the grated matured cheese just until combined, do not over knead. Put the dough in the refrigerator for about 30 minutes.
Roll the dough to 4 mm thickness and cut into small rectangles, about 1x5 cm. Lift rectangles onto greased cookie tray, brush each one with the extra yolk and sprinkle with grated cheddar.
Bake cookies until done evenly, about 27-35 minutes. Don't forget to rotate trays two-three times during baking. Cookies are done if the center is no longer darker in color.