1. Activate the Starter and Combine Wet Ingredients: In a large mixing bowl, combine the active sourdough starter, warm milk, granulated sugar, egg, and vanilla extract. Whisk these ingredients together until they are well combined and the sugar has dissolved. The mixture should look slightly frothy.

2. Mix in Dry Ingredients: Gradually add the all-purpose flour and salt to the wet mixture. Use a wooden spoon or your hands to mix until a shaggy dough forms. It doesn’t need to be perfectly smooth at this stage.

3. Incorporate the Butter: Add the softened unsalted butter to the dough. Knead the dough in the bowl or on a lightly floured surface for about 5-7 minutes until the butter is fully incorporated and the dough becomes smoother and more elastic. It might feel a bit sticky at first, but keep kneading.

4. Add Chocolate Chips and First Rise: Gently fold in the chocolate chips until they are evenly distributed throughout the dough. Form the dough into a ball, place it back in the clean bowl, cover it with plastic wrap or a damp kitchen towel, and let it rise in a warm place for 4-6 hours, or until it has doubled in size.

5. Shape the Loaf and Second Rise: Once the dough has doubled, gently punch it down to release the air. Turn it out onto a lightly floured surface and shape it into a loaf. You can make a round boule or an oblong loaf to fit a loaf pan. Place the shaped dough into a greased loaf pan or onto a baking sheet lined with parchment paper. Cover it again and let it rise for another 1-2 hours, or until it looks puffy and has nearly doubled again.

6. Preheat Oven and Bake: While the dough is on its second rise, preheat your oven to 375 F (190 C). Once the oven is hot and the dough is ready, you can optionally brush the top of the loaf with a little milk or an egg wash for a golden crust.

7. Bake to Golden Perfection: Bake for 35-40 minutes, or until the crust is golden brown and the internal temperature reaches 200-210 F (93-99 C) when checked with an instant-read thermometer. If the top starts to brown too quickly, you can loosely tent it with aluminum foil.

8. Cool Before Slicing: Remove the bread from the oven and transfer it to a wire rack to cool completely before slicing. This is crucial for the texture to set properly and prevents a gummy interior.