10:00 PM: In a small glass jar, whisk 10g of starter culture into 20g of water. Stir in 50g of bread flour and knead by hand briefly into a tight ball. Roll tightly, press down into your jar, cover, and leave to ferment at 72–74°F (22–23°C) overnight until it expands 2 to 3 times its volume.

Prepare the Tangzhong by combining 20g of flour and 100g of boiling water in a small saucepan over medium heat. Whisk continuously until a thick, shiny paste forms. Transfer to a small bowl, cover with plastic wrap touching the surface, and let cool completely overnight.

8:00 AM: In your stand mixer bowl, combine the mature stiff starter, cooled Tangzhong paste, whole milk, egg, bread flour, sugar, carrot juice (if using), and optional instant yeast. Mix on low just until a shaggy dough forms, then cover and allow to autolyse for 30 minutes.

8:30 AM: Turn the mixer onto low speed for 2 to 3 minutes (or speed 3 on a KitchenAid for 3 to 4 minutes) until well-incorporated. Sprinkle in the 7g of salt and mix for 2 more minutes until a solid dough ball begins to form around the hook.

With the mixer still running, add the softened butter in small chunks. Increase to a medium-high speed and knead for 10 to 15 minutes. The dough must fully come together, clearing the bottom and sides of the bowl. (If it remains too sticky after 12 minutes, add 10g to 20g of additional flour).

9:00 AM: Shape the dough into a smooth ball, cover, and place it into a warm proofing area at 76–80°F (24–28°C) for 3 to 4 hours. Perform two separate stretch-and-fold sessions during the first 2 hours of this bulk rise.

12:00 PM: Once the dough feels noticeably light and slightly puffy, transfer the covered container directly into the refrigerator for an extended cold fermentation until the following morning.

Prepare the filling by mixing the wild blueberries, 80g of sugar, lemon zest, and lemon juice in a saucepan over medium-high heat. Bring to a simmer, allowing the berry juices to burst and bubble. Stir in the combined 1 tbsp cornstarch and 1 tbsp sugar mixture, cooking for 1 to 2 minutes until it thickens into a glossy paste. Remove from heat and cool completely.

7:00 AM (Day 3): Lightly dust your work surface with flour. Turn out the cold dough and use a rolling pin to flatten it into an even 15×15 inch square.

Spread the cooled blueberry filling evenly across the surface, leaving a clean 1/2-inch border at the top edge. Roll the dough tightly upward from the bottom into a uniform log.

Using a sharp serrated knife or unflavored dental floss, cut the log into 2-inch wide pieces. Place the individual rolls onto a baking tray lined with parchment paper. (To maintain perfectly round shapes, place them inside individual greased tart rings).

Cover loosely and allow the rolls to proof at room temperature for 1 to 2 hours until they have visibly doubled in size and feel pillowy.

Preheat your oven to 375°F (190°C). Bake the sweet rolls for 22 to 25 minutes until the tops are a beautiful light golden brown. Let cool slightly on a wire rack before drizzling with cream cheese icing or a simple white glaze.