Follow these straightforward steps to create mouthwatering Sourdough Cinnamon Rolls:

1. Mix the Dough: In a large bowl, combine the active sourdough starter, warmed milk, granulated sugar, melted butter, and egg. Stir until well mixed.
2. Add Dry Ingredients: Gradually add the flour and salt to the wet ingredients, mixing until a shaggy dough forms.
3. Knead the Dough: Turn the dough onto a floured surface and knead for about 8-10 minutes until smooth and elastic. Add more flour if necessary.
4. First Rise: Place the dough in a greased bowl, cover with a damp cloth, and let it rise in a warm place for 4-8 hours, or until doubled in size.
5. Prepare the Filling: In a small bowl, mix the softened butter, brown sugar, and cinnamon until combined.
6. Roll Out the Dough: Once the dough has risen, turn it out onto a floured surface and roll it into a rectangle about 1/4 inch thick.
7. Spread the Filling: Evenly spread the cinnamon filling over the rolled-out dough, leaving a small border around the edges.
8. Roll the Dough: Starting from one long edge, tightly roll the dough into a log shape. Pinch the seam to seal it.
9. Cut the Rolls: Using a sharp knife or dental floss, cut the rolled dough into 12 equal pieces.
10. Second Rise: Place the cut rolls in a greased baking dish, cover with a cloth, and let them rise for another 1-2 hours, or until puffy.
11. Preheat the Oven: Preheat your oven to 350°F (175°C).
12. Bake the Rolls: Bake the rolls in the preheated oven for 25-30 minutes or until golden brown.
13. Prepare the Glaze: While the rolls are baking, whisk together powdered sugar, milk, and vanilla extract in a bowl until smooth.
14. Glaze the Rolls: Once baked, remove the rolls from the oven and let them cool slightly. Drizzle the glaze over the warm rolls before serving.