Make the Blueberry Filling

• In a saucepan, combine blueberries, 3 tbsp brown sugar, lemon juice, and water.
• Cook over medium heat until bubbling.
• Mix cornstarch with 2 tsp water and stir it into the blueberries.
• Continue stirring until thickened (about 1–2 minutes).
• Transfer to a bowl and cool completely in the fridge. Reserve 1–2 tbsp for the frosting.

Prepare the Tangzhong

• In a small saucepan, whisk together water and flour until smooth.
• Cook over medium heat, stirring constantly, until the mixture thickens into a paste (1–2 minutes).
• Remove from heat and allow to cool to room temperature.

Make the Dough

• In the bowl of a stand mixer fitted with a dough hook, combine flour, sugar, yeast, and salt.
• Add the milk, egg, cooled tangzhong, and vanilla extract. Mix on low until combined.
• Increase speed to medium and knead for 5–6 minutes, until the dough is smooth.
• Add softened butter a tablespoon at a time, mixing until fully incorporated.
• Knead an additional 5–6 minutes until dough is elastic and pulls away from the sides of the bowl.
• Transfer dough to a greased bowl, cover, and let rise in a warm place for 1 to 1.5 hours, or until doubled in size.

Make the Cinnamon Sugar Butter

• In a bowl, mix the ½ cup dark brown sugar, cinnamon, and 4 tbsp softened butter until smooth.

Assemble the Rolls

• Once risen, punch down the dough and roll out on a lightly floured surface to a 14×20-inch rectangle.
• Spread the cinnamon sugar butter evenly over the dough.
• Spoon the cooled blueberry mixture evenly on top.
• Carefully roll the dough tightly from the long side into a log.
• Cut into 12 even rolls and place into a greased 9×13-inch baking pan.
• Cover and let rise again for 30–45 minutes until puffy.

Bake

• Preheat oven to 350°F (177°C).
• Bake for 25–28 minutes or until lightly golden and centers are cooked through.
• Let cool slightly before frosting.

Make the Frosting

• In a mixing bowl, beat cream cheese and butter until smooth.
• Add powdered sugar, reserved blueberry filling, and heavy cream. Beat until fluffy and light.
• Spread or drizzle over warm rolls.