Dough:

1. In a mixing bowl, combine warm milk, granulated sugar, and active dry yeast. Stir until dissolved and let it sit for 8–10 minutes, or until it becomes foamy.
2. To the sponge, add the egg, all-purpose flour, granulated sugar, salt, and butter. Knead for about 20 minutes until the dough is soft and elastic.
3. Proof the dough for 1 hour and 30 minutes in a warm spot at around 27°C (80–85°F).
4. While the dough is proofing, prepare the caramel.

Salted Caramel sauce:

1. In a pan over medium-low heat, add the granulated sugar and stir with a silicone spatula. Once the sugar has melted and turned golden brown, turn off the stove and add the butter. It may look split at first. Return the pan to the stove, add the heavy whipping cream, and stir until smooth and fully combined. Add flaky salt, let it cool slightly, and strain to remove any lumps. Reserve some caramel for decoration.

Assemble: 

1. Roll out the dough, spread the caramel evenly on top, and sprinkle with cinnamon. Cut the dough into strips with a knife, then roll each strip individually.
2. Place the rolls in a baking pan and proof for 30 minutes at around 27°C (80–85°F).

Bake:

1. Preheat the oven to 180°C (350°F). Pour heavy cream and bake for 20–25 minutes, checking at the 20-minute mark.
2. Warm the reserved caramel slightly on the stove, drizzle it over the baked rolls, sprinkle with flaky salt, and enjoy once slightly cooled.