1. Combine sourdough starter, lukewarm milk, and sugar; stir until dissolved.

2. Add eggs and softened butter; mix until creamy.

3. Gradually add bread flour and salt; knead 8–10 minutes until smooth and elastic.

4. Transfer dough to a greased bowl, cover, and ferment at room temperature for 4–6 hours until puffy.

5. Deflate dough, cover, and refrigerate for 8–12 hours for cold fermentation.

6. Let dough rest 20–30 minutes at room temperature.

7. Roll dough into a 12 x 18 inch rectangle.

8. Spread chocolate hazelnut spread evenly, leaving a 1/2 inch border.

9. Sprinkle dark chocolate chips and chopped hazelnuts over the filling.

10. Roll dough tightly into a log, seal the seam, and place seam-side down.

11. Slice log lengthwise into two halves and twist the strands together.

12. Transfer twisted log into a parchment-lined loaf pan.

13. Proof for 3–5 hours until the dough is puffy.

14. Preheat oven to 350°F (175°C) and bake for 35–40 minutes.

15. Simmer water and sugar to make syrup; brush over hot loaf.

16. Cool loaf for at least 30 minutes before slicing.