1. Prepare the Dough

In a large mixing bowl, combine the sourdough starter, warm milk, and sugar. Stir the mixture until the sugar dissolves. The warm milk helps to activate the sourdough, allowing it to ferment and rise properly.

Next, add the softened butter and mix it into the wet ingredients until fully incorporated. Add the eggs one at a time, mixing well after each addition. The eggs provide structure and richness to the dough.

In a separate bowl, whisk together the flour, salt, cinnamon, and vanilla extract. Gradually add the dry ingredients to the wet ingredients, mixing until a sticky dough forms. You may need to use your hands or a spatula to finish incorporating the flour.

2. Knead the Dough

Turn the dough out onto a lightly floured surface and knead for about 8-10 minutes, or until the dough becomes smooth and elastic. If the dough is too sticky, sprinkle a little more flour on the surface, but try not to add too much. The dough should be soft but not overly sticky.

Once the dough is kneaded, place it in a lightly oiled bowl and cover with a clean kitchen towel or plastic wrap. Let the dough rise in a warm place for about 1-2 hours, or until it has doubled in size. This step is crucial for the dough to become fluffy and tender.

3. Make the Cinnamon Filling

While the dough is rising, prepare the cinnamon filling. In a medium bowl, combine the softened butter, brown sugar, cinnamon, and nutmeg (if using). Mix until the ingredients form a smooth, spreadable paste. Set the filling aside.

4. Roll Out the Dough

Once the dough has doubled in size, punch it down to release any air bubbles and turn it out onto a lightly floured surface. Roll the dough into a rectangle that is approximately 16×12 inches (40×30 cm). You want the dough to be an even thickness throughout.

5. Spread the Cinnamon Filling

Using a spatula or the back of a spoon, spread the cinnamon filling evenly over the surface of the dough, leaving about 1 inch (2.5 cm) on the edges. Be generous with the filling, as it’s what gives these cinnamon rolls their signature flavor.

6. Roll and Slice the Dough

Starting from one of the long sides, carefully roll the dough up tightly into a log. Try to keep the roll as tight as possible to avoid gaps in the filling. Once the dough is fully rolled, pinch the seams together to seal the roll.

Using a sharp knife or dental floss, slice the dough into 12 even rolls. You can adjust the size of the rolls to suit your preference, but 12 rolls is the typical amount for a standard 9×13-inch baking dish.

7. Second Rise

Grease a 9×13-inch baking dish with butter or non-stick spray. Place the sliced cinnamon rolls into the dish, ensuring they are close together but not touching. Cover the dish with a kitchen towel and let the rolls rise for another 30-45 minutes, or until they have puffed up and are touching each other.

8. Bake the Cinnamon Rolls

Preheat your oven to 350°F (175°C). Once the rolls have completed their second rise, place the baking dish in the preheated oven and bake for 25-30 minutes, or until the rolls are golden brown on top and cooked through. If the rolls are browning too quickly, you can cover them loosely with aluminum foil and continue baking until done.

Once baked, remove the rolls from the oven and allow them to cool for about 10 minutes before icing.

9. Make the Icing

While the rolls are cooling, prepare the icing. In a small bowl, whisk together the powdered sugar, milk or cream, vanilla extract, and a pinch of salt. Adjust the consistency by adding more milk if you prefer a thinner glaze, or more powdered sugar if you like a thicker icing.

Drizzle the icing over the warm cinnamon rolls just before serving.