1. Feed sourdough starter 6–8 hours before mixing until doubled in size and floating.

2. In a mixer bowl combine flour, sugar, and salt.

3. Whisk eggs, milk, and vanilla separately and add to dry ingredients with starter.

4. Mix on low until a rough dough forms, then add butter in portions and knead 10–12 minutes until elastic.

5. Fold in orange zest and chocolate chips evenly.

6. Let dough rise in an oiled bowl at 25 °C for 4–6 hours or refrigerate overnight.

7. Shape dough into a round and place in a panettone mold.

8. Proof in a warm spot for 4–5 hours until 1 inch below mold rim.

9. Preheat oven to 175 °C, score top, and bake 40–45 minutes, tenting with foil after 25 minutes.

10. Invert loaf on skewers immediately and hang upside down until fully cooled, about 6 hours.

11. Wrap cooled panettone in parchment and plastic and rest 24 hours before slicing.