1. Place the flour in a bowl and press out a hollow. Heat the milk and saffron until lukewarm. Mix half of the milk with the yeast, pour into the hollow in the flour and sprinkle a tablespoon of sugar on top. Cover and leave to prove for around 10 minutes, until bubbles start to form. Whisk the rest of milk with the butter and egg.
2.Then add the remaining sugar, vanilla sugar and salt. Add it all to the sponge mixture and knead into a smooth yeast dough. Cover and leave to prove again for around 30 minutes in a warm place, until the dough has doubled in size. Briefly knead the yeast dough on a floured working surface and divide into 24 portions. Shape each portion of dough into a thin cylinder of around 15 cm. Curl the ends into a spiral shape and place 1 raisin in the centre of each one. Arrange on a baking tray covered with baking paper and leave to prove for around 10 minutes. Whisk the egg yolk with the milk and brush over the 'lussekatter' buns. Bake on the middle shelf of a preheated oven for approximately 18 minutes at 180° until golden-brown. Leave to cool on a rack.
Preparation time, not including waiting time, around 1 hour.