Evening before: sieve (or sift) 2/3 of the flour into a large bowl and make a well in the center.
Crumble the fresh yeast into a cup, then mix with 1 teaspoon sugar and roughly half of the lukewarm milk. Stir until combined.
Pour the yeast mixture into the flour well, then sprinkle roughly 1-2 tablespoons flour over the top. Let rise for 10-15 minutes until the flour layer cracks.
Add the remaining sugar, remaining milk, salt, and melted butter around the edge of the bowl.
Beat vigorously with a wooden spoon until the dough bubbles and pulls away from the sides of the bowl.
Knead in the remaining flour and raisins, then knead well on a lightly floured surface for 8-10 minutes until smooth.
Divide the dough in half.
From the first half, roll out 3 strands each 35 cm long and braid them together.
From 2/3 of the second half, roll out 3 more strands of 35 cm each and braid them together, then place this smaller braid on top of the first one.
From the remaining dough, roll 2 strands of 35 cm each, twist them around each other like a rope, and place on top.
Place the braided loaf on a lightly floured board or baking tray, cover loosely with a plastic bag, and refrigerate for 8-12 hours.
In the morning, remove from refrigerator and let rise at room temperature for 30 minutes.
Preheat oven to 200 °C (392 °F). Place the braided loaf on the lowest oven rack and bake for 25-30 minutes until golden brown.