Cloud-soft, buttery brioche enriched with eggs and milk meets tangy sourdough, spiraled with warm cinnamon sugar and finished with a silky cream cheese icing.
Begin with an active, bubbly starter at or near peak. Add sourdough starter, bread flour, all-purpose flour, sugar, eggs, salt, milk, and butter to a stand mixer fitted with a dough hook. Knead until smooth and glossy, about 10–15 minutes. Do not add extra flour.
Cover the bowl and place in a warm spot to rise 6–8 hours, or until doubled in size.
Make the filling: In a bowl, stir together softened butter, brown sugar, and cinnamon until smooth.
Lightly flour a work surface and roll the dough into a large rectangle about 1/4 inch thick.
Spread the cinnamon filling evenly over the dough. Roll up tightly from a long side and pinch the seam to seal.
Slice into 12 even rolls. Place in a well-seasoned 14-inch cast iron skillet or baking dish. Cover and let rise until doubled, about 2–6 hours.
Preheat the oven to 375°F. Bake 20–25 minutes, until lightly browned and cooked through. Let cool slightly before frosting.
Make the icing: In a medium saucepan over medium heat, combine cream cheese, heavy cream, honey (or maple syrup), and vanilla extract; stir until smooth (use an immersion blender for extra smoothness if desired). Drizzle over warm rolls and serve.