1. 1. Activate the Starter and Mix Wet Ingredients: In a large mixing bowl, combine the active sourdough starter, warm milk, granulated sugar, egg, melted butter, and vanilla extract. Whisk everything together until it’s well combined and the sugar has dissolved. The mixture should look slightly milky and uniform.

2. 2. Combine Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, salt, and instant yeast (if using). Make sure the salt and yeast are evenly distributed throughout the flour.

3. 3. Form the Dough: Gradually add the dry ingredients to the wet ingredients, mixing with a wooden spoon or your hands until a shaggy dough forms. Once most of the flour is incorporated, turn the dough out onto a lightly floured surface.

4. 4. Knead the Dough: Knead the dough for 8-10 minutes until it becomes smooth, elastic, and no longer sticky. If using a stand mixer with a dough hook, knead on medium-low speed for 6-8 minutes. The dough should pass the “windowpane test” – you should be able to stretch a small piece thin enough to see light through it without tearing.

5. 5. First Rise (Bulk Fermentation): Place the kneaded dough in a lightly oiled bowl, turning it once to coat. Cover the bowl with plastic wrap or a damp kitchen towel and let it rise in a warm place until doubled in size. This will take 2-4 hours with instant yeast, or 8-12 hours (or overnight) if relying solely on sourdough.

6. 6. Incorporate Fillings and Shape: Once the dough has doubled, gently punch it down. Turn it out onto a lightly floured surface and flatten it into a large rectangle, about 12×16 inches. Spread the softened peanut butter evenly over the dough, leaving a small border around the edges. Sprinkle the chocolate chips over the peanut butter. Starting from one of the longer sides, tightly roll the dough into a log. Pinch the seam closed to seal.

7. 7. Second Rise (Proofing): Carefully transfer the rolled dough into a greased 9×5-inch loaf pan. Cover the pan loosely with plastic wrap or a damp towel and let it rise again in a warm place for another 1-2 hours, or until it has almost doubled in size and looks puffy.

8. 8. Bake the Loaf: Preheat your oven to 375 F (190 C). Once preheated, bake the loaf for 35-40 minutes, or until the top is golden brown and the internal temperature reaches 200-210 F (93-99 C) with an instant-read thermometer. If the top starts to brown too quickly, you can loosely tent it with aluminum foil.

9. 9. Cool Before Slicing: Remove the loaf from the oven and let it cool in the pan for 10-15 minutes before transferring it to a wire rack to cool completely. Slicing too early can result in a gummy texture.