Make the Dough: In a large bowl, mix the warm milk, sourdough starter, and sugar until the sugar dissolves. Add the butter, eggs, and vanilla extract, and stir until combined. Gradually add the flour and salt, mixing until the dough begins to come together. Knead the dough for 8-10 minutes until smooth and elastic. Let it rise in a lightly greased bowl, covered with a towel, for 4-6 hours, or until doubled in size.

1. Prepare the Apple Filling: In a small pan, melt 1 tablespoon of butter over medium heat. Add the diced apples, sugar, and cinnamon. Stir occasionally and cook until the apples are soft and caramelized, about 5-7 minutes. Remove from heat and set aside to cool.
2. Assemble the Cinnamon Roll Roses: Punch down the dough and roll it out into a 12×16 inch rectangle. Spread softened butter over the dough. In a small bowl, mix brown sugar and cinnamon, then sprinkle it evenly over the buttered dough. Evenly distribute the cooled apple filling over the cinnamon-sugar layer. Roll the dough tightly from one long edge and slice into 8-10 equal pieces. Shape each slice into a rose by pulling apart the edges while keeping the center slightly open. Place them in a greased round baking dish or on a parchment-lined baking sheet.
3. Let the Dough Rise: Cover the rolls with a clean towel and let them rise for another hour, or until puffy and doubled in size.
4. Bake: Preheat the oven to 350°F (175°C). Bake the rolls for 25-30 minutes, or until golden brown and the apples are bubbling.
5. Make the Glaze (Optional): While the rolls bake, mix powdered sugar, milk, and vanilla extract until smooth. Drizzle over the rolls once they’ve cooled slightly.
6. Serve: Serve warm with a hot drink of your choice and enjoy!