In a bowl, combine lukewarm milk, yeast, and sugar. Stir and let sit for 5–10 minutes until it bubbles.
Stir in the egg, melted butter, and yogurt. Mix well.
Add flour, cocoa powder, corn starch, and salt. Mix and knead for 8–10 minutes (using a mixer) or 10–15 minutes by hand until the dough is very soft. Cover and let rise until doubled in size (about 1–1.5 hours).
In a small bowl, mix the soft butter, brown sugar, cocoa powder, and cinnamon (if using) until smooth.
Once dough has risen, punch it down and roll it into a 13×14-inch rectangle. Evenly spread the filling over the dough.
Cut the dough into 2.5-inch strips. Roll each strip tightly and place them in a greased 10×6-inch baking dish.
Cover the rolls and let them rise for 30–45 minutes until they’re puffy and nearly doubled in size.
Pour a little heavy cream over and between the rolls before baking.
Bake at 175°C (350°F) for 25–30 minutes until the rolls are set and slightly golden.
For Ganache Frosting, heat the heavy cream until warm and steamy. Pour it over chopped dark and milk chocolate. Let it rest for 1 minute, then stir until smooth.
Whisk in softened cream cheese and a pinch of salt until silky.
Chill the ganache for 10–15 minutes until thickened. Lightly whisk by hand before spreading over the warm rolls.
