1. 1. Prepare the Dough (Evening): In a large mixing bowl, combine the warm milk, granulated sugar, and instant yeast. Stir gently and let it sit for 5 minutes until the yeast becomes foamy, indicating it’s active. Add the sourdough discard, melted butter, and egg, mixing until well combined. Gradually add the flour and salt, mixing with a wooden spoon or your hands until a shaggy dough forms.

2. 2. Knead the Dough: Turn the dough out onto a lightly floured surface. Knead for 5-7 minutes until the dough is smooth and elastic. It should be slightly tacky but not sticky. If it’s too sticky, add a tiny bit more flour, one tablespoon at a time.

3. 3. First Rise (Overnight Chill): Lightly grease a clean bowl with oil. Place the dough in the bowl, turning it once to coat. Cover the bowl tightly with plastic wrap and refrigerate for 8-12 hours, or overnight. This slow, cold fermentation develops flavor and makes the dough easier to handle.

4. 4. Shape the Rolls (Morning): The next morning, remove the dough from the refrigerator. On a lightly floured surface, roll the chilled dough into a large rectangle, approximately 12×18 inches. It should be about 1/4 inch thick.

5. 5. Add the Filling: In a small bowl, combine the brown sugar and ground cinnamon. Spread the softened butter evenly over the rolled-out dough, leaving a small border along one long edge. Sprinkle the cinnamon-sugar mixture generously over the butter.

6. 6. Roll and Slice: Starting from one of the long edges, tightly roll the dough into a log. Pinch the seam closed to seal. Using a sharp knife or unflavored dental floss, cut the log into 12 equal slices, each about 1 1/2 inches thick.

7. 7. Second Rise and Bake: Arrange the sliced rolls in a lightly greased 9×13-inch baking dish, leaving a little space between each. Cover the dish loosely with plastic wrap or a clean kitchen towel and let them rise in a warm place for 1 to 1.5 hours, or until they look puffy and have nearly doubled in size. Preheat your oven to 375 F (190 C) during the last 15 minutes of proofing. Bake for 20-25 minutes, or until the tops are golden brown and the rolls are cooked through.

8. 8. Prepare the Icing and Serve: While the rolls are baking, prepare the cream cheese icing. In a medium bowl, beat the softened cream cheese and butter together until smooth. Gradually add the powdered sugar, vanilla extract, and milk/cream, beating until the icing is light and fluffy. Once the rolls are out of the oven, let them cool for 5-10 minutes, then generously spread the cream cheese icing over the warm rolls. Serve immediately and enjoy!