Mix the flour, salt and yeast in a bowl. Mix in the butter and milk, knead into a soft, smooth dough. Cover and leave to rise at room temperature for approx. 1 hr.
Divide the dough into 10 portions, roll out into ovals approx. 1 cm thick. Cut 4 slits (approx. 5 cm long), place the pieces of dough on two sheets of baking paper, carefully pull apart the slits to make the openings wider. Leave to rise for a further 15 mins., brush with the egg yolk, sprinkle with the caraway seeds, slide the baking paper onto the back of a baking tray.
Approx. 12 mins. per tray in the centre of an oven preheated to 230°C. Remove from the oven, leave to cool on a cooling rack.