1. Prepare the Dough: In a large mixing bowl, combine the all-purpose flour, granulated sugar, and salt. Mix well.
2. Combine Wet Ingredients: In another bowl, whisk together the lukewarm milk, pumpkin puree, eggs, and sourdough starter until smooth.
3. Incorporate the Dough: Gradually add the wet mixture to the dry ingredients, mixing until a rough dough forms.
4. Knead the Dough: Transfer the dough to a floured surface and knead for about 8-10 minutes until it becomes smooth and elastic.
5. First Rise: Place the kneaded dough in a lightly greased bowl, cover with a damp cloth, and let it rise in a warm area for 4-6 hours or until doubled in size.
6. Prepare the Filling: In a small bowl, mix the brown sugar, cinnamon, nutmeg, and optional chopped nuts.
7. Shape the Dough: Once risen, punch down the dough and roll it out into a rectangle, about 1/4 inch thick.
8. Spread Filling: Evenly spread the filling mixture over the dough, leaving a small border around the edges.
9. Roll the Dough: Starting from the long edge, roll the dough tightly into a log.
10. Braid the Dough: Cut the log in half lengthwise, revealing the swirls. Twist the two halves together to form a braid, placing it in a greased loaf pan.
11. Second Rise: Cover the braided loaf with a kitchen towel and let it rise again for about 1-2 hours.
12. Preheat Oven: While the loaf rises, preheat your oven to 350°F (175°C).
13. Bake: Once dough has risen, bake the babka in the preheated oven for 30-35 minutes, until golden brown.
14. Cool: Allow the loaf to cool in the pan for 20 minutes, then carefully transfer to a wire rack.
15. Glaze (optional): Mix powdered sugar with milk for a simple glaze and drizzle over the warm babka.

By following these steps, you’ll create a stunning Pumpkin Sourdough Babka that is sure to impress!