Make a tangzhong roux by whisking 25g bread flour and ½ cup water, then cooking on medium-low heat while stirring until thickened to a pudding consistency.
In a large bowl, mix 475g bread flour, 1.5 tsp salt, 1 Tbs white sugar, ¼ cup grapeseed oil, and 2 Tbs starter. Add the cooled tangzhong roux and ¾ cup room temperature water, mixing until no dry flour remains.
Let the dough rest for 30-60 minutes, then knead gently to smooth out any clumps. Perform gentle folds every 2-3 hours throughout the day to develop the gluten.
In the evening, lightly grease a baking pan. Make the cinnamon filling by mixing 4 Tbs softened salted butter, ⅓ cup dark brown sugar, and 1 Tbs cinnamon.
Roll out the dough and spread the cinnamon filling evenly. Roll up the dough tightly and cut into 9 pieces. Place the rolls in the prepared pan and let proof overnight at room temperature.
In the morning, brush the tops of the rolls with 2-3 Tbs melted butter. Bake at 325°F for 35-40 minutes until lightly browned.
Make the cream cheese icing by mixing 4 Tbs salted butter, 4 oz cream cheese, 1 cup powdered sugar, and 2 tsp vanilla paste or extract.
Apply the icing to the warm rolls so it melts into the layers.
