Gently heat the milk to 115°F—this warm temperature is key to activating the yeast.
Sprinkle the yeast over the warmed milk and let it sit until it becomes foamy—this may take about 5-10 minutes.
In a stand mixer, combine the foamy yeast mixture with melted butter, egg, and egg yolk to create a rich base for the dough.
Gradually stir in the bread flour and kosher salt until a sticky dough forms—don’t worry if it’s a bit messy!
Knead the dough for 8-10 minutes until it’s elastic and smooth, adding flour as needed to prevent sticking.
Place the dough in a greased bowl, cover with a towel, and let rise in a warm spot until doubled in size, taking about 1 to 1½ hours.
Roll the dough out, spread softened butter for the filling, sprinkle with dark brown sugar and cinnamon, then roll tightly into a log and slice into rolls.
Arrange the sliced rolls in a greased baking dish and let them rise until puffy, about 45 minutes to 1 hour.
Preheat the oven to 350°F and bake the rolls for 20-25 minutes, until golden brown and fragrant.
Allow rolls to cool for about 10 minutes before preparing the frosting and generously spreading it over the warm rolls.
Notes
Store cinnamon rolls in an airtight container at room temperature for up to 3 days. For longer storage, freeze rolls individually wrapped in plastic wrap and then in a freezer-safe bag for up to 3 months.