Activate yeast: Add 1 tablespoon white sugar to the milk and microwave for 40–45 seconds, until lightly warm but not hot. Stir in the yeast, mix well, and let sit until frothy, about 1–2 minutes.
Make the dough: In a large bowl, combine bread flour and all-purpose flour. Add the frothy milk mixture, sour cream, melted butter, brown sugar, eggs, vanilla, and salt. Mix until combined, then knead until smooth, soft, and slightly tacky.
First rise: Transfer the dough to a greased bowl, cover, and let rise in a warm spot until doubled in size, about 1 hour.
Make the filling: In a small bowl, mix melted salted butter with brown sugar and cinnamon until it forms a thick, spreadable paste.
Roll and fill: Roll the dough into a large rectangle. Spread the cinnamon-butter mixture evenly over the surface, then roll it up tightly and slice into equal rolls (about 10).
Second rise: Arrange rolls in a greased 9×13″ baking dish, cover, and let rise again until puffy, about 30 minutes.
Cream pour: Warm the heavy cream slightly (microwave for about 20 seconds) and pour over the rolls just before baking.
Bake: Bake at 350°F for 30-35 minutes, or until golden and the centers are set but still soft. Tent with foil if browning too quickly.
Frosting: Beat cream cheese and butter until smooth. Add vanilla, heavy cream, and powdered sugar, mixing until creamy and spreadable. Let the rolls cool for about 10-15 minutes before frosting. They should still be warm so the icing melts into every swirl.