Please read through the entire instructions prior to starting!
Start the dough: Warm the milk in the microwave for 45 seconds until the bowl is like a warm bath. You can also warm it on the stovetop. Transfer the warm milk to a large bowl and sprinkle the yeast on top. Add the sugar, egg yolk, egg, and melted butter. Mix until well combined with a wooden spoon. It's important to use a wooden spoon to not kill the yeast. Then, slowly add in the flour and salt and continue to mix until a rough dough forms.
Knead the dough: Now it's time to knead the dough. You can either use the dough hook on your electric mixer for 3-4 minutes (just until a smooth ball forms) or transfer the dough onto a smooth and flour-dusted surface to knead it into a smooth ball by hand (about 5-7 minutes). If it's too sticky, add 2 tablespoons of flour at a time.
Let the dough rise (1 of 2): Transfer the now stiff dough ball to a well-oiled metal or glass bowl. Roll the dough in the oil to help it not harden while it rises and cover it with a light towel. Place this bowl into the oven (it needs to be in a warm place) and turn the oven light on. Allow the dough to rise for 3-4 hours or until it doubles in size.While the dough rises, make the cinnamon sugar filling by mixing the brown sugar and cinnamon. Also, set out the butter for the filling to soften.Expert tip for overnight rise: If you want to leave the dough to rise overnight, let it rise in the fridge for at least 12 hours. Make the rolls: After the dough has doubled, transfer it to a well-floured surface (enough flour to not stick) and roll it into a 14x9-inch rectangle. Spread the softened butter over the dough, leaving a ¼ inch margin at the far edge of the dough.Sprinkle with the cinnamon sugar filling. Roll the dough tightly starting from the 9” side and ending seam side down.
Let the rolls rise (2 of 2): Use a serrated knife to cut 9 even-sized rolls and place them into a greased 9x9 pan or 9" round pan (you can also line the pan with parchment paper instead of greasing). Cover rolls with a towel and place them back in the oven with the light on to rise for another 30 minutes. Or, you can leave them in the sun to rise.
Bake: Next, remove cinnamon rolls from the oven and preheat the oven to 350 degrees. Remove the towel from the rolls and bake for 20-25 minutes until just golden brown. We want them gooey because they'll continue to cook after being removed from the oven. Allow cooling for 10 minutes before frosting.
Frost: Make the frosting by mixing the softened butter, vanilla, powdered sugar, a little salt, and a splash of milk in a large mixing bowl. Spread or drizzle this over the top of the rolls. Enjoy!