Combine milk and vinegar to make soured milk and set aside for 5 minutes.
Sift flour and baking powder in a large bowl. Add in sugar, vanilla sugar and salt.
Cut the cold butter in cubes and rub in with the dry ingredients using your finger tips until the mixture resembles coarse breadcrumbs. Try to work quickly, few bigger lumps of butter are better than over mixing! Place in freezer for a few minutes if the mixture starts getting warm!
Add in the soured milk and egg to the flour mixture. Combine all the ingredients with an electric mixer (dough-hooks on) just enough to form a dough. Again, if the dough feels sticky, place in freezer for a while!
Also add in the cranberries and transfer the dough onto a lightly floured surface.
Cut the dough in half.
Stack the two halves on each other and press down with your hands.
Again cut the dough in half and stack the two parts on each other. Pat down and repeat the procedure one more time.
Form the dough into a rectangle (about 2,5 cm thick and 6 cm in width).
Brush with beaten egg yolk and sprinkle extra sugar on top.
Cut into small triangles. Transfer to the freezer for 10 min.
Bake in preheated oven at 200 C for 20 - 25 minutes until golden and slightly crispy on top.