1. Feed the sourdough starter 6–8 hours before mixing so it is active and bubbly

2. Combine starter, milk, granulated sugar, egg, and egg yolk in a bowl and mix until smooth

3. Add flour and salt and knead until a rough dough forms

4. Gradually add softened butter and continue kneading for 8–10 minutes until elastic

5. Cover and bulk ferment at room temperature for 3–4 hours until the dough rises by about 30–50%

6. Refrigerate the dough overnight for 8–12 hours to chill

7. Melt butter and chopped dark chocolate together, then stir in cocoa powder and powdered sugar until smooth

8. Roll chilled dough on a floured surface into a 10×14 inch rectangle

9. Spread the chocolate filling over the dough leaving a 1/2 inch border

10. Sprinkle chocolate chips over the filling

11. Roll the dough tightly from the short end into a log

12. Slice the log lengthwise and twist the halves with the cut sides facing up

13. Place the twisted loaf into a greased 9×4 inch pan and cover to proof for 6–8 hours until puffy

14. Preheat oven to 375°F (190°C) and brush the loaf with egg wash if desired

15. Bake for 35–40 minutes until the top is deeply golden and the internal temperature reaches 195°F (90°C)

16. Simmer granulated sugar and water to make a syrup and brush over the hot loaf for a glossy finish

17. Cool in pan for 15 minutes then transfer to a rack to cool completely

18. Store at room temperature in an airtight container for up to three days or freeze slices for up to one month